1 /*
2 * Copyright (c) 2001, 2016, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/symbolTable.hpp"
29 #include "classfile/systemDictionary.hpp"
30 #include "code/codeCache.hpp"
31 #include "gc/cms/cmsCollectorPolicy.hpp"
32 #include "gc/cms/cmsOopClosures.inline.hpp"
33 #include "gc/cms/compactibleFreeListSpace.hpp"
34 #include "gc/cms/concurrentMarkSweepGeneration.inline.hpp"
35 #include "gc/cms/concurrentMarkSweepThread.hpp"
36 #include "gc/cms/parNewGeneration.hpp"
37 #include "gc/cms/vmCMSOperations.hpp"
38 #include "gc/serial/genMarkSweep.hpp"
39 #include "gc/serial/tenuredGeneration.hpp"
40 #include "gc/shared/adaptiveSizePolicy.hpp"
41 #include "gc/shared/cardGeneration.inline.hpp"
42 #include "gc/shared/cardTableRS.hpp"
43 #include "gc/shared/collectedHeap.inline.hpp"
44 #include "gc/shared/collectorCounters.hpp"
45 #include "gc/shared/collectorPolicy.hpp"
46 #include "gc/shared/gcLocker.inline.hpp"
47 #include "gc/shared/gcPolicyCounters.hpp"
48 #include "gc/shared/gcTimer.hpp"
49 #include "gc/shared/gcTrace.hpp"
50 #include "gc/shared/gcTraceTime.inline.hpp"
51 #include "gc/shared/genCollectedHeap.hpp"
52 #include "gc/shared/genOopClosures.inline.hpp"
53 #include "gc/shared/isGCActiveMark.hpp"
54 #include "gc/shared/referencePolicy.hpp"
55 #include "gc/shared/strongRootsScope.hpp"
56 #include "gc/shared/taskqueue.inline.hpp"
57 #include "logging/log.hpp"
58 #include "memory/allocation.hpp"
59 #include "memory/iterator.inline.hpp"
60 #include "memory/padded.hpp"
61 #include "memory/resourceArea.hpp"
62 #include "oops/oop.inline.hpp"
63 #include "prims/jvmtiExport.hpp"
64 #include "runtime/atomic.inline.hpp"
65 #include "runtime/globals_extension.hpp"
66 #include "runtime/handles.inline.hpp"
67 #include "runtime/java.hpp"
68 #include "runtime/orderAccess.inline.hpp"
69 #include "runtime/timer.hpp"
70 #include "runtime/vmThread.hpp"
71 #include "services/memoryService.hpp"
72 #include "services/runtimeService.hpp"
73 #include "utilities/stack.inline.hpp"
74
75 // statics
76 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
77 bool CMSCollector::_full_gc_requested = false;
78 GCCause::Cause CMSCollector::_full_gc_cause = GCCause::_no_gc;
79
80 //////////////////////////////////////////////////////////////////
81 // In support of CMS/VM thread synchronization
82 //////////////////////////////////////////////////////////////////
83 // We split use of the CGC_lock into 2 "levels".
84 // The low-level locking is of the usual CGC_lock monitor. We introduce
85 // a higher level "token" (hereafter "CMS token") built on top of the
86 // low level monitor (hereafter "CGC lock").
87 // The token-passing protocol gives priority to the VM thread. The
88 // CMS-lock doesn't provide any fairness guarantees, but clients
89 // should ensure that it is only held for very short, bounded
90 // durations.
91 //
92 // When either of the CMS thread or the VM thread is involved in
93 // collection operations during which it does not want the other
94 // thread to interfere, it obtains the CMS token.
95 //
96 // If either thread tries to get the token while the other has
97 // it, that thread waits. However, if the VM thread and CMS thread
98 // both want the token, then the VM thread gets priority while the
99 // CMS thread waits. This ensures, for instance, that the "concurrent"
100 // phases of the CMS thread's work do not block out the VM thread
101 // for long periods of time as the CMS thread continues to hog
102 // the token. (See bug 4616232).
103 //
104 // The baton-passing functions are, however, controlled by the
105 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
106 // and here the low-level CMS lock, not the high level token,
107 // ensures mutual exclusion.
108 //
109 // Two important conditions that we have to satisfy:
110 // 1. if a thread does a low-level wait on the CMS lock, then it
111 // relinquishes the CMS token if it were holding that token
112 // when it acquired the low-level CMS lock.
113 // 2. any low-level notifications on the low-level lock
114 // should only be sent when a thread has relinquished the token.
115 //
116 // In the absence of either property, we'd have potential deadlock.
117 //
118 // We protect each of the CMS (concurrent and sequential) phases
119 // with the CMS _token_, not the CMS _lock_.
120 //
121 // The only code protected by CMS lock is the token acquisition code
122 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
123 // baton-passing code.
124 //
125 // Unfortunately, i couldn't come up with a good abstraction to factor and
126 // hide the naked CGC_lock manipulation in the baton-passing code
127 // further below. That's something we should try to do. Also, the proof
128 // of correctness of this 2-level locking scheme is far from obvious,
129 // and potentially quite slippery. We have an uneasy suspicion, for instance,
130 // that there may be a theoretical possibility of delay/starvation in the
131 // low-level lock/wait/notify scheme used for the baton-passing because of
132 // potential interference with the priority scheme embodied in the
133 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
134 // invocation further below and marked with "XXX 20011219YSR".
135 // Indeed, as we note elsewhere, this may become yet more slippery
136 // in the presence of multiple CMS and/or multiple VM threads. XXX
137
138 class CMSTokenSync: public StackObj {
139 private:
140 bool _is_cms_thread;
141 public:
142 CMSTokenSync(bool is_cms_thread):
143 _is_cms_thread(is_cms_thread) {
144 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
145 "Incorrect argument to constructor");
146 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
147 }
148
149 ~CMSTokenSync() {
150 assert(_is_cms_thread ?
151 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
152 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
153 "Incorrect state");
154 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
155 }
156 };
157
158 // Convenience class that does a CMSTokenSync, and then acquires
159 // upto three locks.
160 class CMSTokenSyncWithLocks: public CMSTokenSync {
161 private:
162 // Note: locks are acquired in textual declaration order
163 // and released in the opposite order
164 MutexLockerEx _locker1, _locker2, _locker3;
165 public:
166 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
167 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
168 CMSTokenSync(is_cms_thread),
169 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
170 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
171 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
172 { }
173 };
174
175
176 //////////////////////////////////////////////////////////////////
177 // Concurrent Mark-Sweep Generation /////////////////////////////
178 //////////////////////////////////////////////////////////////////
179
180 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
181
182 // This struct contains per-thread things necessary to support parallel
183 // young-gen collection.
184 class CMSParGCThreadState: public CHeapObj<mtGC> {
185 public:
186 CompactibleFreeListSpaceLAB lab;
187 PromotionInfo promo;
188
189 // Constructor.
190 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
191 promo.setSpace(cfls);
192 }
193 };
194
195 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
196 ReservedSpace rs, size_t initial_byte_size, CardTableRS* ct) :
197 CardGeneration(rs, initial_byte_size, ct),
198 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
199 _did_compact(false)
200 {
201 HeapWord* bottom = (HeapWord*) _virtual_space.low();
202 HeapWord* end = (HeapWord*) _virtual_space.high();
203
204 _direct_allocated_words = 0;
205 NOT_PRODUCT(
206 _numObjectsPromoted = 0;
207 _numWordsPromoted = 0;
208 _numObjectsAllocated = 0;
209 _numWordsAllocated = 0;
210 )
211
212 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end));
213 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
214 _cmsSpace->_old_gen = this;
215
216 _gc_stats = new CMSGCStats();
217
218 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
219 // offsets match. The ability to tell free chunks from objects
220 // depends on this property.
221 debug_only(
222 FreeChunk* junk = NULL;
223 assert(UseCompressedClassPointers ||
224 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
225 "Offset of FreeChunk::_prev within FreeChunk must match"
226 " that of OopDesc::_klass within OopDesc");
227 )
228
229 _par_gc_thread_states = NEW_C_HEAP_ARRAY(CMSParGCThreadState*, ParallelGCThreads, mtGC);
230 for (uint i = 0; i < ParallelGCThreads; i++) {
231 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
232 }
233
234 _incremental_collection_failed = false;
235 // The "dilatation_factor" is the expansion that can occur on
236 // account of the fact that the minimum object size in the CMS
237 // generation may be larger than that in, say, a contiguous young
238 // generation.
239 // Ideally, in the calculation below, we'd compute the dilatation
240 // factor as: MinChunkSize/(promoting_gen's min object size)
241 // Since we do not have such a general query interface for the
242 // promoting generation, we'll instead just use the minimum
243 // object size (which today is a header's worth of space);
244 // note that all arithmetic is in units of HeapWords.
245 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
246 assert(_dilatation_factor >= 1.0, "from previous assert");
247 }
248
249
250 // The field "_initiating_occupancy" represents the occupancy percentage
251 // at which we trigger a new collection cycle. Unless explicitly specified
252 // via CMSInitiatingOccupancyFraction (argument "io" below), it
253 // is calculated by:
254 //
255 // Let "f" be MinHeapFreeRatio in
256 //
257 // _initiating_occupancy = 100-f +
258 // f * (CMSTriggerRatio/100)
259 // where CMSTriggerRatio is the argument "tr" below.
260 //
261 // That is, if we assume the heap is at its desired maximum occupancy at the
262 // end of a collection, we let CMSTriggerRatio of the (purported) free
263 // space be allocated before initiating a new collection cycle.
264 //
265 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
266 assert(io <= 100 && tr <= 100, "Check the arguments");
267 if (io >= 0) {
268 _initiating_occupancy = (double)io / 100.0;
269 } else {
270 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
271 (double)(tr * MinHeapFreeRatio) / 100.0)
272 / 100.0;
273 }
274 }
275
276 void ConcurrentMarkSweepGeneration::ref_processor_init() {
277 assert(collector() != NULL, "no collector");
278 collector()->ref_processor_init();
279 }
280
281 void CMSCollector::ref_processor_init() {
282 if (_ref_processor == NULL) {
283 // Allocate and initialize a reference processor
284 _ref_processor =
285 new ReferenceProcessor(_span, // span
286 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
287 ParallelGCThreads, // mt processing degree
288 _cmsGen->refs_discovery_is_mt(), // mt discovery
289 MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
290 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
291 &_is_alive_closure); // closure for liveness info
292 // Initialize the _ref_processor field of CMSGen
293 _cmsGen->set_ref_processor(_ref_processor);
294
295 }
296 }
297
298 AdaptiveSizePolicy* CMSCollector::size_policy() {
299 GenCollectedHeap* gch = GenCollectedHeap::heap();
300 return gch->gen_policy()->size_policy();
301 }
302
303 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
304
305 const char* gen_name = "old";
306 GenCollectorPolicy* gcp = GenCollectedHeap::heap()->gen_policy();
307 // Generation Counters - generation 1, 1 subspace
308 _gen_counters = new GenerationCounters(gen_name, 1, 1,
309 gcp->min_old_size(), gcp->max_old_size(), &_virtual_space);
310
311 _space_counters = new GSpaceCounters(gen_name, 0,
312 _virtual_space.reserved_size(),
313 this, _gen_counters);
314 }
315
316 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
317 _cms_gen(cms_gen)
318 {
319 assert(alpha <= 100, "bad value");
320 _saved_alpha = alpha;
321
322 // Initialize the alphas to the bootstrap value of 100.
323 _gc0_alpha = _cms_alpha = 100;
324
325 _cms_begin_time.update();
326 _cms_end_time.update();
327
328 _gc0_duration = 0.0;
329 _gc0_period = 0.0;
330 _gc0_promoted = 0;
331
332 _cms_duration = 0.0;
333 _cms_period = 0.0;
334 _cms_allocated = 0;
335
336 _cms_used_at_gc0_begin = 0;
337 _cms_used_at_gc0_end = 0;
338 _allow_duty_cycle_reduction = false;
339 _valid_bits = 0;
340 }
341
342 double CMSStats::cms_free_adjustment_factor(size_t free) const {
343 // TBD: CR 6909490
344 return 1.0;
345 }
346
347 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
348 }
349
350 // If promotion failure handling is on use
351 // the padded average size of the promotion for each
352 // young generation collection.
353 double CMSStats::time_until_cms_gen_full() const {
354 size_t cms_free = _cms_gen->cmsSpace()->free();
355 GenCollectedHeap* gch = GenCollectedHeap::heap();
356 size_t expected_promotion = MIN2(gch->young_gen()->capacity(),
357 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
358 if (cms_free > expected_promotion) {
359 // Start a cms collection if there isn't enough space to promote
360 // for the next young collection. Use the padded average as
361 // a safety factor.
362 cms_free -= expected_promotion;
363
364 // Adjust by the safety factor.
365 double cms_free_dbl = (double)cms_free;
366 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor) / 100.0;
367 // Apply a further correction factor which tries to adjust
368 // for recent occurance of concurrent mode failures.
369 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
370 cms_free_dbl = cms_free_dbl * cms_adjustment;
371
372 log_trace(gc)("CMSStats::time_until_cms_gen_full: cms_free " SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
373 cms_free, expected_promotion);
374 log_trace(gc)(" cms_free_dbl %f cms_consumption_rate %f", cms_free_dbl, cms_consumption_rate() + 1.0);
375 // Add 1 in case the consumption rate goes to zero.
376 return cms_free_dbl / (cms_consumption_rate() + 1.0);
377 }
378 return 0.0;
379 }
380
381 // Compare the duration of the cms collection to the
382 // time remaining before the cms generation is empty.
383 // Note that the time from the start of the cms collection
384 // to the start of the cms sweep (less than the total
385 // duration of the cms collection) can be used. This
386 // has been tried and some applications experienced
387 // promotion failures early in execution. This was
388 // possibly because the averages were not accurate
389 // enough at the beginning.
390 double CMSStats::time_until_cms_start() const {
391 // We add "gc0_period" to the "work" calculation
392 // below because this query is done (mostly) at the
393 // end of a scavenge, so we need to conservatively
394 // account for that much possible delay
395 // in the query so as to avoid concurrent mode failures
396 // due to starting the collection just a wee bit too
397 // late.
398 double work = cms_duration() + gc0_period();
399 double deadline = time_until_cms_gen_full();
400 // If a concurrent mode failure occurred recently, we want to be
401 // more conservative and halve our expected time_until_cms_gen_full()
402 if (work > deadline) {
403 log_develop_trace(gc)("CMSCollector: collect because of anticipated promotion before full %3.7f + %3.7f > %3.7f ",
404 cms_duration(), gc0_period(), time_until_cms_gen_full());
405 return 0.0;
406 }
407 return work - deadline;
408 }
409
410 #ifndef PRODUCT
411 void CMSStats::print_on(outputStream *st) const {
412 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
413 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
414 gc0_duration(), gc0_period(), gc0_promoted());
415 st->print(",cms_dur=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
416 cms_duration(), cms_period(), cms_allocated());
417 st->print(",cms_since_beg=%g,cms_since_end=%g",
418 cms_time_since_begin(), cms_time_since_end());
419 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
420 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
421
422 if (valid()) {
423 st->print(",promo_rate=%g,cms_alloc_rate=%g",
424 promotion_rate(), cms_allocation_rate());
425 st->print(",cms_consumption_rate=%g,time_until_full=%g",
426 cms_consumption_rate(), time_until_cms_gen_full());
427 }
428 st->cr();
429 }
430 #endif // #ifndef PRODUCT
431
432 CMSCollector::CollectorState CMSCollector::_collectorState =
433 CMSCollector::Idling;
434 bool CMSCollector::_foregroundGCIsActive = false;
435 bool CMSCollector::_foregroundGCShouldWait = false;
436
437 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
438 CardTableRS* ct,
439 ConcurrentMarkSweepPolicy* cp):
440 _cmsGen(cmsGen),
441 _ct(ct),
442 _ref_processor(NULL), // will be set later
443 _conc_workers(NULL), // may be set later
444 _abort_preclean(false),
445 _start_sampling(false),
446 _between_prologue_and_epilogue(false),
447 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
448 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
449 -1 /* lock-free */, "No_lock" /* dummy */),
450 _modUnionClosurePar(&_modUnionTable),
451 // Adjust my span to cover old (cms) gen
452 _span(cmsGen->reserved()),
453 // Construct the is_alive_closure with _span & markBitMap
454 _is_alive_closure(_span, &_markBitMap),
455 _restart_addr(NULL),
456 _overflow_list(NULL),
457 _stats(cmsGen),
458 _eden_chunk_lock(new Mutex(Mutex::leaf + 1, "CMS_eden_chunk_lock", true,
459 //verify that this lock should be acquired with safepoint check.
460 Monitor::_safepoint_check_sometimes)),
461 _eden_chunk_array(NULL), // may be set in ctor body
462 _eden_chunk_capacity(0), // -- ditto --
463 _eden_chunk_index(0), // -- ditto --
464 _survivor_plab_array(NULL), // -- ditto --
465 _survivor_chunk_array(NULL), // -- ditto --
466 _survivor_chunk_capacity(0), // -- ditto --
467 _survivor_chunk_index(0), // -- ditto --
468 _ser_pmc_preclean_ovflw(0),
469 _ser_kac_preclean_ovflw(0),
470 _ser_pmc_remark_ovflw(0),
471 _par_pmc_remark_ovflw(0),
472 _ser_kac_ovflw(0),
473 _par_kac_ovflw(0),
474 #ifndef PRODUCT
475 _num_par_pushes(0),
476 #endif
477 _collection_count_start(0),
478 _verifying(false),
479 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
480 _completed_initialization(false),
481 _collector_policy(cp),
482 _should_unload_classes(CMSClassUnloadingEnabled),
483 _concurrent_cycles_since_last_unload(0),
484 _roots_scanning_options(GenCollectedHeap::SO_None),
485 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
486 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
487 _gc_tracer_cm(new (ResourceObj::C_HEAP, mtGC) CMSTracer()),
488 _gc_timer_cm(new (ResourceObj::C_HEAP, mtGC) ConcurrentGCTimer()),
489 _cms_start_registered(false)
490 {
491 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
492 ExplicitGCInvokesConcurrent = true;
493 }
494 // Now expand the span and allocate the collection support structures
495 // (MUT, marking bit map etc.) to cover both generations subject to
496 // collection.
497
498 // For use by dirty card to oop closures.
499 _cmsGen->cmsSpace()->set_collector(this);
500
501 // Allocate MUT and marking bit map
502 {
503 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
504 if (!_markBitMap.allocate(_span)) {
505 log_warning(gc)("Failed to allocate CMS Bit Map");
506 return;
507 }
508 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
509 }
510 {
511 _modUnionTable.allocate(_span);
512 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
513 }
514
515 if (!_markStack.allocate(MarkStackSize)) {
516 log_warning(gc)("Failed to allocate CMS Marking Stack");
517 return;
518 }
519
520 // Support for multi-threaded concurrent phases
521 if (CMSConcurrentMTEnabled) {
522 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
523 // just for now
524 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3) / 4);
525 }
526 if (ConcGCThreads > 1) {
527 _conc_workers = new YieldingFlexibleWorkGang("CMS Thread",
528 ConcGCThreads, true);
529 if (_conc_workers == NULL) {
530 log_warning(gc)("GC/CMS: _conc_workers allocation failure: forcing -CMSConcurrentMTEnabled");
531 CMSConcurrentMTEnabled = false;
532 } else {
533 _conc_workers->initialize_workers();
534 }
535 } else {
536 CMSConcurrentMTEnabled = false;
537 }
538 }
539 if (!CMSConcurrentMTEnabled) {
540 ConcGCThreads = 0;
541 } else {
542 // Turn off CMSCleanOnEnter optimization temporarily for
543 // the MT case where it's not fixed yet; see 6178663.
544 CMSCleanOnEnter = false;
545 }
546 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
547 "Inconsistency");
548
549 // Parallel task queues; these are shared for the
550 // concurrent and stop-world phases of CMS, but
551 // are not shared with parallel scavenge (ParNew).
552 {
553 uint i;
554 uint num_queues = MAX2(ParallelGCThreads, ConcGCThreads);
555
556 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
557 || ParallelRefProcEnabled)
558 && num_queues > 0) {
559 _task_queues = new OopTaskQueueSet(num_queues);
560 if (_task_queues == NULL) {
561 log_warning(gc)("task_queues allocation failure.");
562 return;
563 }
564 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
565 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
566 for (i = 0; i < num_queues; i++) {
567 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
568 if (q == NULL) {
569 log_warning(gc)("work_queue allocation failure.");
570 return;
571 }
572 _task_queues->register_queue(i, q);
573 }
574 for (i = 0; i < num_queues; i++) {
575 _task_queues->queue(i)->initialize();
576 _hash_seed[i] = 17; // copied from ParNew
577 }
578 }
579 }
580
581 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
582
583 // Clip CMSBootstrapOccupancy between 0 and 100.
584 _bootstrap_occupancy = CMSBootstrapOccupancy / 100.0;
585
586 // Now tell CMS generations the identity of their collector
587 ConcurrentMarkSweepGeneration::set_collector(this);
588
589 // Create & start a CMS thread for this CMS collector
590 _cmsThread = ConcurrentMarkSweepThread::start(this);
591 assert(cmsThread() != NULL, "CMS Thread should have been created");
592 assert(cmsThread()->collector() == this,
593 "CMS Thread should refer to this gen");
594 assert(CGC_lock != NULL, "Where's the CGC_lock?");
595
596 // Support for parallelizing young gen rescan
597 GenCollectedHeap* gch = GenCollectedHeap::heap();
598 assert(gch->young_gen()->kind() == Generation::ParNew, "CMS can only be used with ParNew");
599 _young_gen = (ParNewGeneration*)gch->young_gen();
600 if (gch->supports_inline_contig_alloc()) {
601 _top_addr = gch->top_addr();
602 _end_addr = gch->end_addr();
603 assert(_young_gen != NULL, "no _young_gen");
604 _eden_chunk_index = 0;
605 _eden_chunk_capacity = (_young_gen->max_capacity() + CMSSamplingGrain) / CMSSamplingGrain;
606 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
607 }
608
609 // Support for parallelizing survivor space rescan
610 if ((CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) || CMSParallelInitialMarkEnabled) {
611 const size_t max_plab_samples =
612 _young_gen->max_survivor_size() / (PLAB::min_size() * HeapWordSize);
613
614 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
615 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
616 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
617 _survivor_chunk_capacity = max_plab_samples;
618 for (uint i = 0; i < ParallelGCThreads; i++) {
619 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
620 ChunkArray* cur = ::new (&_survivor_plab_array[i]) ChunkArray(vec, max_plab_samples);
621 assert(cur->end() == 0, "Should be 0");
622 assert(cur->array() == vec, "Should be vec");
623 assert(cur->capacity() == max_plab_samples, "Error");
624 }
625 }
626
627 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
628 _gc_counters = new CollectorCounters("CMS", 1);
629 _completed_initialization = true;
630 _inter_sweep_timer.start(); // start of time
631 }
632
633 const char* ConcurrentMarkSweepGeneration::name() const {
634 return "concurrent mark-sweep generation";
635 }
636 void ConcurrentMarkSweepGeneration::update_counters() {
637 if (UsePerfData) {
638 _space_counters->update_all();
639 _gen_counters->update_all();
640 }
641 }
642
643 // this is an optimized version of update_counters(). it takes the
644 // used value as a parameter rather than computing it.
645 //
646 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
647 if (UsePerfData) {
648 _space_counters->update_used(used);
649 _space_counters->update_capacity();
650 _gen_counters->update_all();
651 }
652 }
653
654 void ConcurrentMarkSweepGeneration::print() const {
655 Generation::print();
656 cmsSpace()->print();
657 }
658
659 #ifndef PRODUCT
660 void ConcurrentMarkSweepGeneration::print_statistics() {
661 cmsSpace()->printFLCensus(0);
662 }
663 #endif
664
665 size_t
666 ConcurrentMarkSweepGeneration::contiguous_available() const {
667 // dld proposes an improvement in precision here. If the committed
668 // part of the space ends in a free block we should add that to
669 // uncommitted size in the calculation below. Will make this
670 // change later, staying with the approximation below for the
671 // time being. -- ysr.
672 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
673 }
674
675 size_t
676 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
677 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
678 }
679
680 size_t ConcurrentMarkSweepGeneration::max_available() const {
681 return free() + _virtual_space.uncommitted_size();
682 }
683
684 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
685 size_t available = max_available();
686 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
687 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
688 log_trace(gc, promotion)("CMS: promo attempt is%s safe: available(" SIZE_FORMAT ") %s av_promo(" SIZE_FORMAT "), max_promo(" SIZE_FORMAT ")",
689 res? "":" not", available, res? ">=":"<", av_promo, max_promotion_in_bytes);
690 return res;
691 }
692
693 // At a promotion failure dump information on block layout in heap
694 // (cms old generation).
695 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
696 Log(gc, promotion) log;
697 if (log.is_trace()) {
698 ResourceMark rm;
699 cmsSpace()->dump_at_safepoint_with_locks(collector(), log.trace_stream());
700 }
701 }
702
703 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
704 // Clear the promotion information. These pointers can be adjusted
705 // along with all the other pointers into the heap but
706 // compaction is expected to be a rare event with
707 // a heap using cms so don't do it without seeing the need.
708 for (uint i = 0; i < ParallelGCThreads; i++) {
709 _par_gc_thread_states[i]->promo.reset();
710 }
711 }
712
713 void ConcurrentMarkSweepGeneration::compute_new_size() {
714 assert_locked_or_safepoint(Heap_lock);
715
716 // If incremental collection failed, we just want to expand
717 // to the limit.
718 if (incremental_collection_failed()) {
719 clear_incremental_collection_failed();
720 grow_to_reserved();
721 return;
722 }
723
724 // The heap has been compacted but not reset yet.
725 // Any metric such as free() or used() will be incorrect.
726
727 CardGeneration::compute_new_size();
728
729 // Reset again after a possible resizing
730 if (did_compact()) {
731 cmsSpace()->reset_after_compaction();
732 }
733 }
734
735 void ConcurrentMarkSweepGeneration::compute_new_size_free_list() {
736 assert_locked_or_safepoint(Heap_lock);
737
738 // If incremental collection failed, we just want to expand
739 // to the limit.
740 if (incremental_collection_failed()) {
741 clear_incremental_collection_failed();
742 grow_to_reserved();
743 return;
744 }
745
746 double free_percentage = ((double) free()) / capacity();
747 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
748 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
749
750 // compute expansion delta needed for reaching desired free percentage
751 if (free_percentage < desired_free_percentage) {
752 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
753 assert(desired_capacity >= capacity(), "invalid expansion size");
754 size_t expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
755 Log(gc) log;
756 if (log.is_trace()) {
757 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
758 log.trace("From compute_new_size: ");
759 log.trace(" Free fraction %f", free_percentage);
760 log.trace(" Desired free fraction %f", desired_free_percentage);
761 log.trace(" Maximum free fraction %f", maximum_free_percentage);
762 log.trace(" Capacity " SIZE_FORMAT, capacity() / 1000);
763 log.trace(" Desired capacity " SIZE_FORMAT, desired_capacity / 1000);
764 GenCollectedHeap* gch = GenCollectedHeap::heap();
765 assert(gch->is_old_gen(this), "The CMS generation should always be the old generation");
766 size_t young_size = gch->young_gen()->capacity();
767 log.trace(" Young gen size " SIZE_FORMAT, young_size / 1000);
768 log.trace(" unsafe_max_alloc_nogc " SIZE_FORMAT, unsafe_max_alloc_nogc() / 1000);
769 log.trace(" contiguous available " SIZE_FORMAT, contiguous_available() / 1000);
770 log.trace(" Expand by " SIZE_FORMAT " (bytes)", expand_bytes);
771 }
772 // safe if expansion fails
773 expand_for_gc_cause(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
774 log.trace(" Expanded free fraction %f", ((double) free()) / capacity());
775 } else {
776 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
777 assert(desired_capacity <= capacity(), "invalid expansion size");
778 size_t shrink_bytes = capacity() - desired_capacity;
779 // Don't shrink unless the delta is greater than the minimum shrink we want
780 if (shrink_bytes >= MinHeapDeltaBytes) {
781 shrink_free_list_by(shrink_bytes);
782 }
783 }
784 }
785
786 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
787 return cmsSpace()->freelistLock();
788 }
789
790 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, bool tlab) {
791 CMSSynchronousYieldRequest yr;
792 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
793 return have_lock_and_allocate(size, tlab);
794 }
795
796 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
797 bool tlab /* ignored */) {
798 assert_lock_strong(freelistLock());
799 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
800 HeapWord* res = cmsSpace()->allocate(adjustedSize);
801 // Allocate the object live (grey) if the background collector has
802 // started marking. This is necessary because the marker may
803 // have passed this address and consequently this object will
804 // not otherwise be greyed and would be incorrectly swept up.
805 // Note that if this object contains references, the writing
806 // of those references will dirty the card containing this object
807 // allowing the object to be blackened (and its references scanned)
808 // either during a preclean phase or at the final checkpoint.
809 if (res != NULL) {
810 // We may block here with an uninitialized object with
811 // its mark-bit or P-bits not yet set. Such objects need
812 // to be safely navigable by block_start().
813 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
814 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
815 collector()->direct_allocated(res, adjustedSize);
816 _direct_allocated_words += adjustedSize;
817 // allocation counters
818 NOT_PRODUCT(
819 _numObjectsAllocated++;
820 _numWordsAllocated += (int)adjustedSize;
821 )
822 }
823 return res;
824 }
825
826 // In the case of direct allocation by mutators in a generation that
827 // is being concurrently collected, the object must be allocated
828 // live (grey) if the background collector has started marking.
829 // This is necessary because the marker may
830 // have passed this address and consequently this object will
831 // not otherwise be greyed and would be incorrectly swept up.
832 // Note that if this object contains references, the writing
833 // of those references will dirty the card containing this object
834 // allowing the object to be blackened (and its references scanned)
835 // either during a preclean phase or at the final checkpoint.
836 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
837 assert(_markBitMap.covers(start, size), "Out of bounds");
838 if (_collectorState >= Marking) {
839 MutexLockerEx y(_markBitMap.lock(),
840 Mutex::_no_safepoint_check_flag);
841 // [see comments preceding SweepClosure::do_blk() below for details]
842 //
843 // Can the P-bits be deleted now? JJJ
844 //
845 // 1. need to mark the object as live so it isn't collected
846 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
847 // 3. need to mark the end of the object so marking, precleaning or sweeping
848 // can skip over uninitialized or unparsable objects. An allocated
849 // object is considered uninitialized for our purposes as long as
850 // its klass word is NULL. All old gen objects are parsable
851 // as soon as they are initialized.)
852 _markBitMap.mark(start); // object is live
853 _markBitMap.mark(start + 1); // object is potentially uninitialized?
854 _markBitMap.mark(start + size - 1);
855 // mark end of object
856 }
857 // check that oop looks uninitialized
858 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
859 }
860
861 void CMSCollector::promoted(bool par, HeapWord* start,
862 bool is_obj_array, size_t obj_size) {
863 assert(_markBitMap.covers(start), "Out of bounds");
864 // See comment in direct_allocated() about when objects should
865 // be allocated live.
866 if (_collectorState >= Marking) {
867 // we already hold the marking bit map lock, taken in
868 // the prologue
869 if (par) {
870 _markBitMap.par_mark(start);
871 } else {
872 _markBitMap.mark(start);
873 }
874 // We don't need to mark the object as uninitialized (as
875 // in direct_allocated above) because this is being done with the
876 // world stopped and the object will be initialized by the
877 // time the marking, precleaning or sweeping get to look at it.
878 // But see the code for copying objects into the CMS generation,
879 // where we need to ensure that concurrent readers of the
880 // block offset table are able to safely navigate a block that
881 // is in flux from being free to being allocated (and in
882 // transition while being copied into) and subsequently
883 // becoming a bona-fide object when the copy/promotion is complete.
884 assert(SafepointSynchronize::is_at_safepoint(),
885 "expect promotion only at safepoints");
886
887 if (_collectorState < Sweeping) {
888 // Mark the appropriate cards in the modUnionTable, so that
889 // this object gets scanned before the sweep. If this is
890 // not done, CMS generation references in the object might
891 // not get marked.
892 // For the case of arrays, which are otherwise precisely
893 // marked, we need to dirty the entire array, not just its head.
894 if (is_obj_array) {
895 // The [par_]mark_range() method expects mr.end() below to
896 // be aligned to the granularity of a bit's representation
897 // in the heap. In the case of the MUT below, that's a
898 // card size.
899 MemRegion mr(start,
900 (HeapWord*)round_to((intptr_t)(start + obj_size),
901 CardTableModRefBS::card_size /* bytes */));
902 if (par) {
903 _modUnionTable.par_mark_range(mr);
904 } else {
905 _modUnionTable.mark_range(mr);
906 }
907 } else { // not an obj array; we can just mark the head
908 if (par) {
909 _modUnionTable.par_mark(start);
910 } else {
911 _modUnionTable.mark(start);
912 }
913 }
914 }
915 }
916 }
917
918 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
919 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
920 // allocate, copy and if necessary update promoinfo --
921 // delegate to underlying space.
922 assert_lock_strong(freelistLock());
923
924 #ifndef PRODUCT
925 if (GenCollectedHeap::heap()->promotion_should_fail()) {
926 return NULL;
927 }
928 #endif // #ifndef PRODUCT
929
930 oop res = _cmsSpace->promote(obj, obj_size);
931 if (res == NULL) {
932 // expand and retry
933 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
934 expand_for_gc_cause(s*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_promotion);
935 // Since this is the old generation, we don't try to promote
936 // into a more senior generation.
937 res = _cmsSpace->promote(obj, obj_size);
938 }
939 if (res != NULL) {
940 // See comment in allocate() about when objects should
941 // be allocated live.
942 assert(obj->is_oop(), "Will dereference klass pointer below");
943 collector()->promoted(false, // Not parallel
944 (HeapWord*)res, obj->is_objArray(), obj_size);
945 // promotion counters
946 NOT_PRODUCT(
947 _numObjectsPromoted++;
948 _numWordsPromoted +=
949 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
950 )
951 }
952 return res;
953 }
954
955
956 // IMPORTANT: Notes on object size recognition in CMS.
957 // ---------------------------------------------------
958 // A block of storage in the CMS generation is always in
959 // one of three states. A free block (FREE), an allocated
960 // object (OBJECT) whose size() method reports the correct size,
961 // and an intermediate state (TRANSIENT) in which its size cannot
962 // be accurately determined.
963 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
964 // -----------------------------------------------------
965 // FREE: klass_word & 1 == 1; mark_word holds block size
966 //
967 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
968 // obj->size() computes correct size
969 //
970 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
971 //
972 // STATE IDENTIFICATION: (64 bit+COOPS)
973 // ------------------------------------
974 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
975 //
976 // OBJECT: klass_word installed; klass_word != 0;
977 // obj->size() computes correct size
978 //
979 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
980 //
981 //
982 // STATE TRANSITION DIAGRAM
983 //
984 // mut / parnew mut / parnew
985 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
986 // ^ |
987 // |------------------------ DEAD <------------------------------------|
988 // sweep mut
989 //
990 // While a block is in TRANSIENT state its size cannot be determined
991 // so readers will either need to come back later or stall until
992 // the size can be determined. Note that for the case of direct
993 // allocation, P-bits, when available, may be used to determine the
994 // size of an object that may not yet have been initialized.
995
996 // Things to support parallel young-gen collection.
997 oop
998 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
999 oop old, markOop m,
1000 size_t word_sz) {
1001 #ifndef PRODUCT
1002 if (GenCollectedHeap::heap()->promotion_should_fail()) {
1003 return NULL;
1004 }
1005 #endif // #ifndef PRODUCT
1006
1007 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1008 PromotionInfo* promoInfo = &ps->promo;
1009 // if we are tracking promotions, then first ensure space for
1010 // promotion (including spooling space for saving header if necessary).
1011 // then allocate and copy, then track promoted info if needed.
1012 // When tracking (see PromotionInfo::track()), the mark word may
1013 // be displaced and in this case restoration of the mark word
1014 // occurs in the (oop_since_save_marks_)iterate phase.
1015 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1016 // Out of space for allocating spooling buffers;
1017 // try expanding and allocating spooling buffers.
1018 if (!expand_and_ensure_spooling_space(promoInfo)) {
1019 return NULL;
1020 }
1021 }
1022 assert(promoInfo->has_spooling_space(), "Control point invariant");
1023 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1024 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1025 if (obj_ptr == NULL) {
1026 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1027 if (obj_ptr == NULL) {
1028 return NULL;
1029 }
1030 }
1031 oop obj = oop(obj_ptr);
1032 OrderAccess::storestore();
1033 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1034 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1035 // IMPORTANT: See note on object initialization for CMS above.
1036 // Otherwise, copy the object. Here we must be careful to insert the
1037 // klass pointer last, since this marks the block as an allocated object.
1038 // Except with compressed oops it's the mark word.
1039 HeapWord* old_ptr = (HeapWord*)old;
1040 // Restore the mark word copied above.
1041 obj->set_mark(m);
1042 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1043 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1044 OrderAccess::storestore();
1045
1046 if (UseCompressedClassPointers) {
1047 // Copy gap missed by (aligned) header size calculation below
1048 obj->set_klass_gap(old->klass_gap());
1049 }
1050 if (word_sz > (size_t)oopDesc::header_size()) {
1051 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1052 obj_ptr + oopDesc::header_size(),
1053 word_sz - oopDesc::header_size());
1054 }
1055
1056 // Now we can track the promoted object, if necessary. We take care
1057 // to delay the transition from uninitialized to full object
1058 // (i.e., insertion of klass pointer) until after, so that it
1059 // atomically becomes a promoted object.
1060 if (promoInfo->tracking()) {
1061 promoInfo->track((PromotedObject*)obj, old->klass());
1062 }
1063 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1064 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1065 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1066
1067 // Finally, install the klass pointer (this should be volatile).
1068 OrderAccess::storestore();
1069 obj->set_klass(old->klass());
1070 // We should now be able to calculate the right size for this object
1071 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1072
1073 collector()->promoted(true, // parallel
1074 obj_ptr, old->is_objArray(), word_sz);
1075
1076 NOT_PRODUCT(
1077 Atomic::inc_ptr(&_numObjectsPromoted);
1078 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1079 )
1080
1081 return obj;
1082 }
1083
1084 void
1085 ConcurrentMarkSweepGeneration::
1086 par_promote_alloc_done(int thread_num) {
1087 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1088 ps->lab.retire(thread_num);
1089 }
1090
1091 void
1092 ConcurrentMarkSweepGeneration::
1093 par_oop_since_save_marks_iterate_done(int thread_num) {
1094 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1095 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1096 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1097 }
1098
1099 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1100 size_t size,
1101 bool tlab)
1102 {
1103 // We allow a STW collection only if a full
1104 // collection was requested.
1105 return full || should_allocate(size, tlab); // FIX ME !!!
1106 // This and promotion failure handling are connected at the
1107 // hip and should be fixed by untying them.
1108 }
1109
1110 bool CMSCollector::shouldConcurrentCollect() {
1111 LogTarget(Trace, gc) log;
1112
1113 if (_full_gc_requested) {
1114 log.print("CMSCollector: collect because of explicit gc request (or GCLocker)");
1115 return true;
1116 }
1117
1118 FreelistLocker x(this);
1119 // ------------------------------------------------------------------
1120 // Print out lots of information which affects the initiation of
1121 // a collection.
1122 if (log.is_enabled() && stats().valid()) {
1123 log.print("CMSCollector shouldConcurrentCollect: ");
1124
1125 LogStream out(log);
1126 stats().print_on(&out);
1127
1128 log.print("time_until_cms_gen_full %3.7f", stats().time_until_cms_gen_full());
1129 log.print("free=" SIZE_FORMAT, _cmsGen->free());
1130 log.print("contiguous_available=" SIZE_FORMAT, _cmsGen->contiguous_available());
1131 log.print("promotion_rate=%g", stats().promotion_rate());
1132 log.print("cms_allocation_rate=%g", stats().cms_allocation_rate());
1133 log.print("occupancy=%3.7f", _cmsGen->occupancy());
1134 log.print("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1135 log.print("cms_time_since_begin=%3.7f", stats().cms_time_since_begin());
1136 log.print("cms_time_since_end=%3.7f", stats().cms_time_since_end());
1137 log.print("metadata initialized %d", MetaspaceGC::should_concurrent_collect());
1138 }
1139 // ------------------------------------------------------------------
1140
1141 // If the estimated time to complete a cms collection (cms_duration())
1142 // is less than the estimated time remaining until the cms generation
1143 // is full, start a collection.
1144 if (!UseCMSInitiatingOccupancyOnly) {
1145 if (stats().valid()) {
1146 if (stats().time_until_cms_start() == 0.0) {
1147 return true;
1148 }
1149 } else {
1150 // We want to conservatively collect somewhat early in order
1151 // to try and "bootstrap" our CMS/promotion statistics;
1152 // this branch will not fire after the first successful CMS
1153 // collection because the stats should then be valid.
1154 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1155 log.print(" CMSCollector: collect for bootstrapping statistics: occupancy = %f, boot occupancy = %f",
1156 _cmsGen->occupancy(), _bootstrap_occupancy);
1157 return true;
1158 }
1159 }
1160 }
1161
1162 // Otherwise, we start a collection cycle if
1163 // old gen want a collection cycle started. Each may use
1164 // an appropriate criterion for making this decision.
1165 // XXX We need to make sure that the gen expansion
1166 // criterion dovetails well with this. XXX NEED TO FIX THIS
1167 if (_cmsGen->should_concurrent_collect()) {
1168 log.print("CMS old gen initiated");
1169 return true;
1170 }
1171
1172 // We start a collection if we believe an incremental collection may fail;
1173 // this is not likely to be productive in practice because it's probably too
1174 // late anyway.
1175 GenCollectedHeap* gch = GenCollectedHeap::heap();
1176 assert(gch->collector_policy()->is_generation_policy(),
1177 "You may want to check the correctness of the following");
1178 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1179 log.print("CMSCollector: collect because incremental collection will fail ");
1180 return true;
1181 }
1182
1183 if (MetaspaceGC::should_concurrent_collect()) {
1184 log.print("CMSCollector: collect for metadata allocation ");
1185 return true;
1186 }
1187
1188 // CMSTriggerInterval starts a CMS cycle if enough time has passed.
1189 if (CMSTriggerInterval >= 0) {
1190 if (CMSTriggerInterval == 0) {
1191 // Trigger always
1192 return true;
1193 }
1194
1195 // Check the CMS time since begin (we do not check the stats validity
1196 // as we want to be able to trigger the first CMS cycle as well)
1197 if (stats().cms_time_since_begin() >= (CMSTriggerInterval / ((double) MILLIUNITS))) {
1198 if (stats().valid()) {
1199 log.print("CMSCollector: collect because of trigger interval (time since last begin %3.7f secs)",
1200 stats().cms_time_since_begin());
1201 } else {
1202 log.print("CMSCollector: collect because of trigger interval (first collection)");
1203 }
1204 return true;
1205 }
1206 }
1207
1208 return false;
1209 }
1210
1211 void CMSCollector::set_did_compact(bool v) { _cmsGen->set_did_compact(v); }
1212
1213 // Clear _expansion_cause fields of constituent generations
1214 void CMSCollector::clear_expansion_cause() {
1215 _cmsGen->clear_expansion_cause();
1216 }
1217
1218 // We should be conservative in starting a collection cycle. To
1219 // start too eagerly runs the risk of collecting too often in the
1220 // extreme. To collect too rarely falls back on full collections,
1221 // which works, even if not optimum in terms of concurrent work.
1222 // As a work around for too eagerly collecting, use the flag
1223 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1224 // giving the user an easily understandable way of controlling the
1225 // collections.
1226 // We want to start a new collection cycle if any of the following
1227 // conditions hold:
1228 // . our current occupancy exceeds the configured initiating occupancy
1229 // for this generation, or
1230 // . we recently needed to expand this space and have not, since that
1231 // expansion, done a collection of this generation, or
1232 // . the underlying space believes that it may be a good idea to initiate
1233 // a concurrent collection (this may be based on criteria such as the
1234 // following: the space uses linear allocation and linear allocation is
1235 // going to fail, or there is believed to be excessive fragmentation in
1236 // the generation, etc... or ...
1237 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1238 // the case of the old generation; see CR 6543076):
1239 // we may be approaching a point at which allocation requests may fail because
1240 // we will be out of sufficient free space given allocation rate estimates.]
1241 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1242
1243 assert_lock_strong(freelistLock());
1244 if (occupancy() > initiating_occupancy()) {
1245 log_trace(gc)(" %s: collect because of occupancy %f / %f ",
1246 short_name(), occupancy(), initiating_occupancy());
1247 return true;
1248 }
1249 if (UseCMSInitiatingOccupancyOnly) {
1250 return false;
1251 }
1252 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1253 log_trace(gc)(" %s: collect because expanded for allocation ", short_name());
1254 return true;
1255 }
1256 return false;
1257 }
1258
1259 void ConcurrentMarkSweepGeneration::collect(bool full,
1260 bool clear_all_soft_refs,
1261 size_t size,
1262 bool tlab)
1263 {
1264 collector()->collect(full, clear_all_soft_refs, size, tlab);
1265 }
1266
1267 void CMSCollector::collect(bool full,
1268 bool clear_all_soft_refs,
1269 size_t size,
1270 bool tlab)
1271 {
1272 // The following "if" branch is present for defensive reasons.
1273 // In the current uses of this interface, it can be replaced with:
1274 // assert(!GCLocker.is_active(), "Can't be called otherwise");
1275 // But I am not placing that assert here to allow future
1276 // generality in invoking this interface.
1277 if (GCLocker::is_active()) {
1278 // A consistency test for GCLocker
1279 assert(GCLocker::needs_gc(), "Should have been set already");
1280 // Skip this foreground collection, instead
1281 // expanding the heap if necessary.
1282 // Need the free list locks for the call to free() in compute_new_size()
1283 compute_new_size();
1284 return;
1285 }
1286 acquire_control_and_collect(full, clear_all_soft_refs);
1287 }
1288
1289 void CMSCollector::request_full_gc(unsigned int full_gc_count, GCCause::Cause cause) {
1290 GenCollectedHeap* gch = GenCollectedHeap::heap();
1291 unsigned int gc_count = gch->total_full_collections();
1292 if (gc_count == full_gc_count) {
1293 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1294 _full_gc_requested = true;
1295 _full_gc_cause = cause;
1296 CGC_lock->notify(); // nudge CMS thread
1297 } else {
1298 assert(gc_count > full_gc_count, "Error: causal loop");
1299 }
1300 }
1301
1302 bool CMSCollector::is_external_interruption() {
1303 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1304 return GCCause::is_user_requested_gc(cause) ||
1305 GCCause::is_serviceability_requested_gc(cause);
1306 }
1307
1308 void CMSCollector::report_concurrent_mode_interruption() {
1309 if (is_external_interruption()) {
1310 log_debug(gc)("Concurrent mode interrupted");
1311 } else {
1312 log_debug(gc)("Concurrent mode failure");
1313 _gc_tracer_cm->report_concurrent_mode_failure();
1314 }
1315 }
1316
1317
1318 // The foreground and background collectors need to coordinate in order
1319 // to make sure that they do not mutually interfere with CMS collections.
1320 // When a background collection is active,
1321 // the foreground collector may need to take over (preempt) and
1322 // synchronously complete an ongoing collection. Depending on the
1323 // frequency of the background collections and the heap usage
1324 // of the application, this preemption can be seldom or frequent.
1325 // There are only certain
1326 // points in the background collection that the "collection-baton"
1327 // can be passed to the foreground collector.
1328 //
1329 // The foreground collector will wait for the baton before
1330 // starting any part of the collection. The foreground collector
1331 // will only wait at one location.
1332 //
1333 // The background collector will yield the baton before starting a new
1334 // phase of the collection (e.g., before initial marking, marking from roots,
1335 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1336 // of the loop which switches the phases. The background collector does some
1337 // of the phases (initial mark, final re-mark) with the world stopped.
1338 // Because of locking involved in stopping the world,
1339 // the foreground collector should not block waiting for the background
1340 // collector when it is doing a stop-the-world phase. The background
1341 // collector will yield the baton at an additional point just before
1342 // it enters a stop-the-world phase. Once the world is stopped, the
1343 // background collector checks the phase of the collection. If the
1344 // phase has not changed, it proceeds with the collection. If the
1345 // phase has changed, it skips that phase of the collection. See
1346 // the comments on the use of the Heap_lock in collect_in_background().
1347 //
1348 // Variable used in baton passing.
1349 // _foregroundGCIsActive - Set to true by the foreground collector when
1350 // it wants the baton. The foreground clears it when it has finished
1351 // the collection.
1352 // _foregroundGCShouldWait - Set to true by the background collector
1353 // when it is running. The foreground collector waits while
1354 // _foregroundGCShouldWait is true.
1355 // CGC_lock - monitor used to protect access to the above variables
1356 // and to notify the foreground and background collectors.
1357 // _collectorState - current state of the CMS collection.
1358 //
1359 // The foreground collector
1360 // acquires the CGC_lock
1361 // sets _foregroundGCIsActive
1362 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1363 // various locks acquired in preparation for the collection
1364 // are released so as not to block the background collector
1365 // that is in the midst of a collection
1366 // proceeds with the collection
1367 // clears _foregroundGCIsActive
1368 // returns
1369 //
1370 // The background collector in a loop iterating on the phases of the
1371 // collection
1372 // acquires the CGC_lock
1373 // sets _foregroundGCShouldWait
1374 // if _foregroundGCIsActive is set
1375 // clears _foregroundGCShouldWait, notifies _CGC_lock
1376 // waits on _CGC_lock for _foregroundGCIsActive to become false
1377 // and exits the loop.
1378 // otherwise
1379 // proceed with that phase of the collection
1380 // if the phase is a stop-the-world phase,
1381 // yield the baton once more just before enqueueing
1382 // the stop-world CMS operation (executed by the VM thread).
1383 // returns after all phases of the collection are done
1384 //
1385
1386 void CMSCollector::acquire_control_and_collect(bool full,
1387 bool clear_all_soft_refs) {
1388 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1389 assert(!Thread::current()->is_ConcurrentGC_thread(),
1390 "shouldn't try to acquire control from self!");
1391
1392 // Start the protocol for acquiring control of the
1393 // collection from the background collector (aka CMS thread).
1394 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1395 "VM thread should have CMS token");
1396 // Remember the possibly interrupted state of an ongoing
1397 // concurrent collection
1398 CollectorState first_state = _collectorState;
1399
1400 // Signal to a possibly ongoing concurrent collection that
1401 // we want to do a foreground collection.
1402 _foregroundGCIsActive = true;
1403
1404 // release locks and wait for a notify from the background collector
1405 // releasing the locks in only necessary for phases which
1406 // do yields to improve the granularity of the collection.
1407 assert_lock_strong(bitMapLock());
1408 // We need to lock the Free list lock for the space that we are
1409 // currently collecting.
1410 assert(haveFreelistLocks(), "Must be holding free list locks");
1411 bitMapLock()->unlock();
1412 releaseFreelistLocks();
1413 {
1414 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1415 if (_foregroundGCShouldWait) {
1416 // We are going to be waiting for action for the CMS thread;
1417 // it had better not be gone (for instance at shutdown)!
1418 assert(ConcurrentMarkSweepThread::cmst() != NULL && !ConcurrentMarkSweepThread::cmst()->has_terminated(),
1419 "CMS thread must be running");
1420 // Wait here until the background collector gives us the go-ahead
1421 ConcurrentMarkSweepThread::clear_CMS_flag(
1422 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1423 // Get a possibly blocked CMS thread going:
1424 // Note that we set _foregroundGCIsActive true above,
1425 // without protection of the CGC_lock.
1426 CGC_lock->notify();
1427 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1428 "Possible deadlock");
1429 while (_foregroundGCShouldWait) {
1430 // wait for notification
1431 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1432 // Possibility of delay/starvation here, since CMS token does
1433 // not know to give priority to VM thread? Actually, i think
1434 // there wouldn't be any delay/starvation, but the proof of
1435 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1436 }
1437 ConcurrentMarkSweepThread::set_CMS_flag(
1438 ConcurrentMarkSweepThread::CMS_vm_has_token);
1439 }
1440 }
1441 // The CMS_token is already held. Get back the other locks.
1442 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1443 "VM thread should have CMS token");
1444 getFreelistLocks();
1445 bitMapLock()->lock_without_safepoint_check();
1446 log_debug(gc, state)("CMS foreground collector has asked for control " INTPTR_FORMAT " with first state %d",
1447 p2i(Thread::current()), first_state);
1448 log_debug(gc, state)(" gets control with state %d", _collectorState);
1449
1450 // Inform cms gen if this was due to partial collection failing.
1451 // The CMS gen may use this fact to determine its expansion policy.
1452 GenCollectedHeap* gch = GenCollectedHeap::heap();
1453 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1454 assert(!_cmsGen->incremental_collection_failed(),
1455 "Should have been noticed, reacted to and cleared");
1456 _cmsGen->set_incremental_collection_failed();
1457 }
1458
1459 if (first_state > Idling) {
1460 report_concurrent_mode_interruption();
1461 }
1462
1463 set_did_compact(true);
1464
1465 // If the collection is being acquired from the background
1466 // collector, there may be references on the discovered
1467 // references lists. Abandon those references, since some
1468 // of them may have become unreachable after concurrent
1469 // discovery; the STW compacting collector will redo discovery
1470 // more precisely, without being subject to floating garbage.
1471 // Leaving otherwise unreachable references in the discovered
1472 // lists would require special handling.
1473 ref_processor()->disable_discovery();
1474 ref_processor()->abandon_partial_discovery();
1475 ref_processor()->verify_no_references_recorded();
1476
1477 if (first_state > Idling) {
1478 save_heap_summary();
1479 }
1480
1481 do_compaction_work(clear_all_soft_refs);
1482
1483 // Has the GC time limit been exceeded?
1484 size_t max_eden_size = _young_gen->max_eden_size();
1485 GCCause::Cause gc_cause = gch->gc_cause();
1486 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1487 _young_gen->eden()->used(),
1488 _cmsGen->max_capacity(),
1489 max_eden_size,
1490 full,
1491 gc_cause,
1492 gch->collector_policy());
1493
1494 // Reset the expansion cause, now that we just completed
1495 // a collection cycle.
1496 clear_expansion_cause();
1497 _foregroundGCIsActive = false;
1498 return;
1499 }
1500
1501 // Resize the tenured generation
1502 // after obtaining the free list locks for the
1503 // two generations.
1504 void CMSCollector::compute_new_size() {
1505 assert_locked_or_safepoint(Heap_lock);
1506 FreelistLocker z(this);
1507 MetaspaceGC::compute_new_size();
1508 _cmsGen->compute_new_size_free_list();
1509 }
1510
1511 // A work method used by the foreground collector to do
1512 // a mark-sweep-compact.
1513 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1514 GenCollectedHeap* gch = GenCollectedHeap::heap();
1515
1516 STWGCTimer* gc_timer = GenMarkSweep::gc_timer();
1517 gc_timer->register_gc_start();
1518
1519 SerialOldTracer* gc_tracer = GenMarkSweep::gc_tracer();
1520 gc_tracer->report_gc_start(gch->gc_cause(), gc_timer->gc_start());
1521
1522 gch->pre_full_gc_dump(gc_timer);
1523
1524 GCTraceTime(Trace, gc, phases) t("CMS:MSC");
1525
1526 // Temporarily widen the span of the weak reference processing to
1527 // the entire heap.
1528 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1529 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1530 // Temporarily, clear the "is_alive_non_header" field of the
1531 // reference processor.
1532 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1533 // Temporarily make reference _processing_ single threaded (non-MT).
1534 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1535 // Temporarily make refs discovery atomic
1536 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1537 // Temporarily make reference _discovery_ single threaded (non-MT)
1538 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1539
1540 ref_processor()->set_enqueuing_is_done(false);
1541 ref_processor()->enable_discovery();
1542 ref_processor()->setup_policy(clear_all_soft_refs);
1543 // If an asynchronous collection finishes, the _modUnionTable is
1544 // all clear. If we are assuming the collection from an asynchronous
1545 // collection, clear the _modUnionTable.
1546 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1547 "_modUnionTable should be clear if the baton was not passed");
1548 _modUnionTable.clear_all();
1549 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1550 "mod union for klasses should be clear if the baton was passed");
1551 _ct->klass_rem_set()->clear_mod_union();
1552
1553 // We must adjust the allocation statistics being maintained
1554 // in the free list space. We do so by reading and clearing
1555 // the sweep timer and updating the block flux rate estimates below.
1556 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1557 if (_inter_sweep_timer.is_active()) {
1558 _inter_sweep_timer.stop();
1559 // Note that we do not use this sample to update the _inter_sweep_estimate.
1560 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1561 _inter_sweep_estimate.padded_average(),
1562 _intra_sweep_estimate.padded_average());
1563 }
1564
1565 GenMarkSweep::invoke_at_safepoint(ref_processor(), clear_all_soft_refs);
1566 #ifdef ASSERT
1567 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
1568 size_t free_size = cms_space->free();
1569 assert(free_size ==
1570 pointer_delta(cms_space->end(), cms_space->compaction_top())
1571 * HeapWordSize,
1572 "All the free space should be compacted into one chunk at top");
1573 assert(cms_space->dictionary()->total_chunk_size(
1574 debug_only(cms_space->freelistLock())) == 0 ||
1575 cms_space->totalSizeInIndexedFreeLists() == 0,
1576 "All the free space should be in a single chunk");
1577 size_t num = cms_space->totalCount();
1578 assert((free_size == 0 && num == 0) ||
1579 (free_size > 0 && (num == 1 || num == 2)),
1580 "There should be at most 2 free chunks after compaction");
1581 #endif // ASSERT
1582 _collectorState = Resetting;
1583 assert(_restart_addr == NULL,
1584 "Should have been NULL'd before baton was passed");
1585 reset_stw();
1586 _cmsGen->reset_after_compaction();
1587 _concurrent_cycles_since_last_unload = 0;
1588
1589 // Clear any data recorded in the PLAB chunk arrays.
1590 if (_survivor_plab_array != NULL) {
1591 reset_survivor_plab_arrays();
1592 }
1593
1594 // Adjust the per-size allocation stats for the next epoch.
1595 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
1596 // Restart the "inter sweep timer" for the next epoch.
1597 _inter_sweep_timer.reset();
1598 _inter_sweep_timer.start();
1599
1600 gch->post_full_gc_dump(gc_timer);
1601
1602 gc_timer->register_gc_end();
1603
1604 gc_tracer->report_gc_end(gc_timer->gc_end(), gc_timer->time_partitions());
1605
1606 // For a mark-sweep-compact, compute_new_size() will be called
1607 // in the heap's do_collection() method.
1608 }
1609
1610 void CMSCollector::print_eden_and_survivor_chunk_arrays() {
1611 Log(gc, heap) log;
1612 if (!log.is_trace()) {
1613 return;
1614 }
1615
1616 ContiguousSpace* eden_space = _young_gen->eden();
1617 ContiguousSpace* from_space = _young_gen->from();
1618 ContiguousSpace* to_space = _young_gen->to();
1619 // Eden
1620 if (_eden_chunk_array != NULL) {
1621 log.trace("eden " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1622 p2i(eden_space->bottom()), p2i(eden_space->top()),
1623 p2i(eden_space->end()), eden_space->capacity());
1624 log.trace("_eden_chunk_index=" SIZE_FORMAT ", _eden_chunk_capacity=" SIZE_FORMAT,
1625 _eden_chunk_index, _eden_chunk_capacity);
1626 for (size_t i = 0; i < _eden_chunk_index; i++) {
1627 log.trace("_eden_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_eden_chunk_array[i]));
1628 }
1629 }
1630 // Survivor
1631 if (_survivor_chunk_array != NULL) {
1632 log.trace("survivor " PTR_FORMAT "-" PTR_FORMAT "-" PTR_FORMAT "(" SIZE_FORMAT ")",
1633 p2i(from_space->bottom()), p2i(from_space->top()),
1634 p2i(from_space->end()), from_space->capacity());
1635 log.trace("_survivor_chunk_index=" SIZE_FORMAT ", _survivor_chunk_capacity=" SIZE_FORMAT,
1636 _survivor_chunk_index, _survivor_chunk_capacity);
1637 for (size_t i = 0; i < _survivor_chunk_index; i++) {
1638 log.trace("_survivor_chunk_array[" SIZE_FORMAT "]=" PTR_FORMAT, i, p2i(_survivor_chunk_array[i]));
1639 }
1640 }
1641 }
1642
1643 void CMSCollector::getFreelistLocks() const {
1644 // Get locks for all free lists in all generations that this
1645 // collector is responsible for
1646 _cmsGen->freelistLock()->lock_without_safepoint_check();
1647 }
1648
1649 void CMSCollector::releaseFreelistLocks() const {
1650 // Release locks for all free lists in all generations that this
1651 // collector is responsible for
1652 _cmsGen->freelistLock()->unlock();
1653 }
1654
1655 bool CMSCollector::haveFreelistLocks() const {
1656 // Check locks for all free lists in all generations that this
1657 // collector is responsible for
1658 assert_lock_strong(_cmsGen->freelistLock());
1659 PRODUCT_ONLY(ShouldNotReachHere());
1660 return true;
1661 }
1662
1663 // A utility class that is used by the CMS collector to
1664 // temporarily "release" the foreground collector from its
1665 // usual obligation to wait for the background collector to
1666 // complete an ongoing phase before proceeding.
1667 class ReleaseForegroundGC: public StackObj {
1668 private:
1669 CMSCollector* _c;
1670 public:
1671 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
1672 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
1673 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1674 // allow a potentially blocked foreground collector to proceed
1675 _c->_foregroundGCShouldWait = false;
1676 if (_c->_foregroundGCIsActive) {
1677 CGC_lock->notify();
1678 }
1679 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1680 "Possible deadlock");
1681 }
1682
1683 ~ReleaseForegroundGC() {
1684 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
1685 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1686 _c->_foregroundGCShouldWait = true;
1687 }
1688 };
1689
1690 void CMSCollector::collect_in_background(GCCause::Cause cause) {
1691 assert(Thread::current()->is_ConcurrentGC_thread(),
1692 "A CMS asynchronous collection is only allowed on a CMS thread.");
1693
1694 GenCollectedHeap* gch = GenCollectedHeap::heap();
1695 {
1696 bool safepoint_check = Mutex::_no_safepoint_check_flag;
1697 MutexLockerEx hl(Heap_lock, safepoint_check);
1698 FreelistLocker fll(this);
1699 MutexLockerEx x(CGC_lock, safepoint_check);
1700 if (_foregroundGCIsActive) {
1701 // The foreground collector is. Skip this
1702 // background collection.
1703 assert(!_foregroundGCShouldWait, "Should be clear");
1704 return;
1705 } else {
1706 assert(_collectorState == Idling, "Should be idling before start.");
1707 _collectorState = InitialMarking;
1708 register_gc_start(cause);
1709 // Reset the expansion cause, now that we are about to begin
1710 // a new cycle.
1711 clear_expansion_cause();
1712
1713 // Clear the MetaspaceGC flag since a concurrent collection
1714 // is starting but also clear it after the collection.
1715 MetaspaceGC::set_should_concurrent_collect(false);
1716 }
1717 // Decide if we want to enable class unloading as part of the
1718 // ensuing concurrent GC cycle.
1719 update_should_unload_classes();
1720 _full_gc_requested = false; // acks all outstanding full gc requests
1721 _full_gc_cause = GCCause::_no_gc;
1722 // Signal that we are about to start a collection
1723 gch->increment_total_full_collections(); // ... starting a collection cycle
1724 _collection_count_start = gch->total_full_collections();
1725 }
1726
1727 size_t prev_used = _cmsGen->used();
1728
1729 // The change of the collection state is normally done at this level;
1730 // the exceptions are phases that are executed while the world is
1731 // stopped. For those phases the change of state is done while the
1732 // world is stopped. For baton passing purposes this allows the
1733 // background collector to finish the phase and change state atomically.
1734 // The foreground collector cannot wait on a phase that is done
1735 // while the world is stopped because the foreground collector already
1736 // has the world stopped and would deadlock.
1737 while (_collectorState != Idling) {
1738 log_debug(gc, state)("Thread " INTPTR_FORMAT " in CMS state %d",
1739 p2i(Thread::current()), _collectorState);
1740 // The foreground collector
1741 // holds the Heap_lock throughout its collection.
1742 // holds the CMS token (but not the lock)
1743 // except while it is waiting for the background collector to yield.
1744 //
1745 // The foreground collector should be blocked (not for long)
1746 // if the background collector is about to start a phase
1747 // executed with world stopped. If the background
1748 // collector has already started such a phase, the
1749 // foreground collector is blocked waiting for the
1750 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
1751 // are executed in the VM thread.
1752 //
1753 // The locking order is
1754 // PendingListLock (PLL) -- if applicable (FinalMarking)
1755 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
1756 // CMS token (claimed in
1757 // stop_world_and_do() -->
1758 // safepoint_synchronize() -->
1759 // CMSThread::synchronize())
1760
1761 {
1762 // Check if the FG collector wants us to yield.
1763 CMSTokenSync x(true); // is cms thread
1764 if (waitForForegroundGC()) {
1765 // We yielded to a foreground GC, nothing more to be
1766 // done this round.
1767 assert(_foregroundGCShouldWait == false, "We set it to false in "
1768 "waitForForegroundGC()");
1769 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1770 p2i(Thread::current()), _collectorState);
1771 return;
1772 } else {
1773 // The background collector can run but check to see if the
1774 // foreground collector has done a collection while the
1775 // background collector was waiting to get the CGC_lock
1776 // above. If yes, break so that _foregroundGCShouldWait
1777 // is cleared before returning.
1778 if (_collectorState == Idling) {
1779 break;
1780 }
1781 }
1782 }
1783
1784 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
1785 "should be waiting");
1786
1787 switch (_collectorState) {
1788 case InitialMarking:
1789 {
1790 ReleaseForegroundGC x(this);
1791 stats().record_cms_begin();
1792 VM_CMS_Initial_Mark initial_mark_op(this);
1793 VMThread::execute(&initial_mark_op);
1794 }
1795 // The collector state may be any legal state at this point
1796 // since the background collector may have yielded to the
1797 // foreground collector.
1798 break;
1799 case Marking:
1800 // initial marking in checkpointRootsInitialWork has been completed
1801 if (markFromRoots()) { // we were successful
1802 assert(_collectorState == Precleaning, "Collector state should "
1803 "have changed");
1804 } else {
1805 assert(_foregroundGCIsActive, "Internal state inconsistency");
1806 }
1807 break;
1808 case Precleaning:
1809 // marking from roots in markFromRoots has been completed
1810 preclean();
1811 assert(_collectorState == AbortablePreclean ||
1812 _collectorState == FinalMarking,
1813 "Collector state should have changed");
1814 break;
1815 case AbortablePreclean:
1816 abortable_preclean();
1817 assert(_collectorState == FinalMarking, "Collector state should "
1818 "have changed");
1819 break;
1820 case FinalMarking:
1821 {
1822 ReleaseForegroundGC x(this);
1823
1824 VM_CMS_Final_Remark final_remark_op(this);
1825 VMThread::execute(&final_remark_op);
1826 }
1827 assert(_foregroundGCShouldWait, "block post-condition");
1828 break;
1829 case Sweeping:
1830 // final marking in checkpointRootsFinal has been completed
1831 sweep();
1832 assert(_collectorState == Resizing, "Collector state change "
1833 "to Resizing must be done under the free_list_lock");
1834
1835 case Resizing: {
1836 // Sweeping has been completed...
1837 // At this point the background collection has completed.
1838 // Don't move the call to compute_new_size() down
1839 // into code that might be executed if the background
1840 // collection was preempted.
1841 {
1842 ReleaseForegroundGC x(this); // unblock FG collection
1843 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
1844 CMSTokenSync z(true); // not strictly needed.
1845 if (_collectorState == Resizing) {
1846 compute_new_size();
1847 save_heap_summary();
1848 _collectorState = Resetting;
1849 } else {
1850 assert(_collectorState == Idling, "The state should only change"
1851 " because the foreground collector has finished the collection");
1852 }
1853 }
1854 break;
1855 }
1856 case Resetting:
1857 // CMS heap resizing has been completed
1858 reset_concurrent();
1859 assert(_collectorState == Idling, "Collector state should "
1860 "have changed");
1861
1862 MetaspaceGC::set_should_concurrent_collect(false);
1863
1864 stats().record_cms_end();
1865 // Don't move the concurrent_phases_end() and compute_new_size()
1866 // calls to here because a preempted background collection
1867 // has it's state set to "Resetting".
1868 break;
1869 case Idling:
1870 default:
1871 ShouldNotReachHere();
1872 break;
1873 }
1874 log_debug(gc, state)(" Thread " INTPTR_FORMAT " done - next CMS state %d",
1875 p2i(Thread::current()), _collectorState);
1876 assert(_foregroundGCShouldWait, "block post-condition");
1877 }
1878
1879 // Should this be in gc_epilogue?
1880 collector_policy()->counters()->update_counters();
1881
1882 {
1883 // Clear _foregroundGCShouldWait and, in the event that the
1884 // foreground collector is waiting, notify it, before
1885 // returning.
1886 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1887 _foregroundGCShouldWait = false;
1888 if (_foregroundGCIsActive) {
1889 CGC_lock->notify();
1890 }
1891 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1892 "Possible deadlock");
1893 }
1894 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " exiting collection CMS state %d",
1895 p2i(Thread::current()), _collectorState);
1896 log_info(gc, heap)("Old: " SIZE_FORMAT "K->" SIZE_FORMAT "K(" SIZE_FORMAT "K)",
1897 prev_used / K, _cmsGen->used()/K, _cmsGen->capacity() /K);
1898 }
1899
1900 void CMSCollector::register_gc_start(GCCause::Cause cause) {
1901 _cms_start_registered = true;
1902 _gc_timer_cm->register_gc_start();
1903 _gc_tracer_cm->report_gc_start(cause, _gc_timer_cm->gc_start());
1904 }
1905
1906 void CMSCollector::register_gc_end() {
1907 if (_cms_start_registered) {
1908 report_heap_summary(GCWhen::AfterGC);
1909
1910 _gc_timer_cm->register_gc_end();
1911 _gc_tracer_cm->report_gc_end(_gc_timer_cm->gc_end(), _gc_timer_cm->time_partitions());
1912 _cms_start_registered = false;
1913 }
1914 }
1915
1916 void CMSCollector::save_heap_summary() {
1917 GenCollectedHeap* gch = GenCollectedHeap::heap();
1918 _last_heap_summary = gch->create_heap_summary();
1919 _last_metaspace_summary = gch->create_metaspace_summary();
1920 }
1921
1922 void CMSCollector::report_heap_summary(GCWhen::Type when) {
1923 _gc_tracer_cm->report_gc_heap_summary(when, _last_heap_summary);
1924 _gc_tracer_cm->report_metaspace_summary(when, _last_metaspace_summary);
1925 }
1926
1927 bool CMSCollector::waitForForegroundGC() {
1928 bool res = false;
1929 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
1930 "CMS thread should have CMS token");
1931 // Block the foreground collector until the
1932 // background collectors decides whether to
1933 // yield.
1934 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1935 _foregroundGCShouldWait = true;
1936 if (_foregroundGCIsActive) {
1937 // The background collector yields to the
1938 // foreground collector and returns a value
1939 // indicating that it has yielded. The foreground
1940 // collector can proceed.
1941 res = true;
1942 _foregroundGCShouldWait = false;
1943 ConcurrentMarkSweepThread::clear_CMS_flag(
1944 ConcurrentMarkSweepThread::CMS_cms_has_token);
1945 ConcurrentMarkSweepThread::set_CMS_flag(
1946 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1947 // Get a possibly blocked foreground thread going
1948 CGC_lock->notify();
1949 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
1950 p2i(Thread::current()), _collectorState);
1951 while (_foregroundGCIsActive) {
1952 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1953 }
1954 ConcurrentMarkSweepThread::set_CMS_flag(
1955 ConcurrentMarkSweepThread::CMS_cms_has_token);
1956 ConcurrentMarkSweepThread::clear_CMS_flag(
1957 ConcurrentMarkSweepThread::CMS_cms_wants_token);
1958 }
1959 log_debug(gc, state)("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
1960 p2i(Thread::current()), _collectorState);
1961 return res;
1962 }
1963
1964 // Because of the need to lock the free lists and other structures in
1965 // the collector, common to all the generations that the collector is
1966 // collecting, we need the gc_prologues of individual CMS generations
1967 // delegate to their collector. It may have been simpler had the
1968 // current infrastructure allowed one to call a prologue on a
1969 // collector. In the absence of that we have the generation's
1970 // prologue delegate to the collector, which delegates back
1971 // some "local" work to a worker method in the individual generations
1972 // that it's responsible for collecting, while itself doing any
1973 // work common to all generations it's responsible for. A similar
1974 // comment applies to the gc_epilogue()'s.
1975 // The role of the variable _between_prologue_and_epilogue is to
1976 // enforce the invocation protocol.
1977 void CMSCollector::gc_prologue(bool full) {
1978 // Call gc_prologue_work() for the CMSGen
1979 // we are responsible for.
1980
1981 // The following locking discipline assumes that we are only called
1982 // when the world is stopped.
1983 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
1984
1985 // The CMSCollector prologue must call the gc_prologues for the
1986 // "generations" that it's responsible
1987 // for.
1988
1989 assert( Thread::current()->is_VM_thread()
1990 || ( CMSScavengeBeforeRemark
1991 && Thread::current()->is_ConcurrentGC_thread()),
1992 "Incorrect thread type for prologue execution");
1993
1994 if (_between_prologue_and_epilogue) {
1995 // We have already been invoked; this is a gc_prologue delegation
1996 // from yet another CMS generation that we are responsible for, just
1997 // ignore it since all relevant work has already been done.
1998 return;
1999 }
2000
2001 // set a bit saying prologue has been called; cleared in epilogue
2002 _between_prologue_and_epilogue = true;
2003 // Claim locks for common data structures, then call gc_prologue_work()
2004 // for each CMSGen.
2005
2006 getFreelistLocks(); // gets free list locks on constituent spaces
2007 bitMapLock()->lock_without_safepoint_check();
2008
2009 // Should call gc_prologue_work() for all cms gens we are responsible for
2010 bool duringMarking = _collectorState >= Marking
2011 && _collectorState < Sweeping;
2012
2013 // The young collections clear the modified oops state, which tells if
2014 // there are any modified oops in the class. The remark phase also needs
2015 // that information. Tell the young collection to save the union of all
2016 // modified klasses.
2017 if (duringMarking) {
2018 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2019 }
2020
2021 bool registerClosure = duringMarking;
2022
2023 _cmsGen->gc_prologue_work(full, registerClosure, &_modUnionClosurePar);
2024
2025 if (!full) {
2026 stats().record_gc0_begin();
2027 }
2028 }
2029
2030 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2031
2032 _capacity_at_prologue = capacity();
2033 _used_at_prologue = used();
2034
2035 // Delegate to CMScollector which knows how to coordinate between
2036 // this and any other CMS generations that it is responsible for
2037 // collecting.
2038 collector()->gc_prologue(full);
2039 }
2040
2041 // This is a "private" interface for use by this generation's CMSCollector.
2042 // Not to be called directly by any other entity (for instance,
2043 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2044 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2045 bool registerClosure, ModUnionClosure* modUnionClosure) {
2046 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2047 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2048 "Should be NULL");
2049 if (registerClosure) {
2050 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2051 }
2052 cmsSpace()->gc_prologue();
2053 // Clear stat counters
2054 NOT_PRODUCT(
2055 assert(_numObjectsPromoted == 0, "check");
2056 assert(_numWordsPromoted == 0, "check");
2057 log_develop_trace(gc, alloc)("Allocated " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes concurrently",
2058 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2059 _numObjectsAllocated = 0;
2060 _numWordsAllocated = 0;
2061 )
2062 }
2063
2064 void CMSCollector::gc_epilogue(bool full) {
2065 // The following locking discipline assumes that we are only called
2066 // when the world is stopped.
2067 assert(SafepointSynchronize::is_at_safepoint(),
2068 "world is stopped assumption");
2069
2070 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2071 // if linear allocation blocks need to be appropriately marked to allow the
2072 // the blocks to be parsable. We also check here whether we need to nudge the
2073 // CMS collector thread to start a new cycle (if it's not already active).
2074 assert( Thread::current()->is_VM_thread()
2075 || ( CMSScavengeBeforeRemark
2076 && Thread::current()->is_ConcurrentGC_thread()),
2077 "Incorrect thread type for epilogue execution");
2078
2079 if (!_between_prologue_and_epilogue) {
2080 // We have already been invoked; this is a gc_epilogue delegation
2081 // from yet another CMS generation that we are responsible for, just
2082 // ignore it since all relevant work has already been done.
2083 return;
2084 }
2085 assert(haveFreelistLocks(), "must have freelist locks");
2086 assert_lock_strong(bitMapLock());
2087
2088 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2089
2090 _cmsGen->gc_epilogue_work(full);
2091
2092 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2093 // in case sampling was not already enabled, enable it
2094 _start_sampling = true;
2095 }
2096 // reset _eden_chunk_array so sampling starts afresh
2097 _eden_chunk_index = 0;
2098
2099 size_t cms_used = _cmsGen->cmsSpace()->used();
2100
2101 // update performance counters - this uses a special version of
2102 // update_counters() that allows the utilization to be passed as a
2103 // parameter, avoiding multiple calls to used().
2104 //
2105 _cmsGen->update_counters(cms_used);
2106
2107 bitMapLock()->unlock();
2108 releaseFreelistLocks();
2109
2110 if (!CleanChunkPoolAsync) {
2111 Chunk::clean_chunk_pool();
2112 }
2113
2114 set_did_compact(false);
2115 _between_prologue_and_epilogue = false; // ready for next cycle
2116 }
2117
2118 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2119 collector()->gc_epilogue(full);
2120
2121 // Also reset promotion tracking in par gc thread states.
2122 for (uint i = 0; i < ParallelGCThreads; i++) {
2123 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2124 }
2125 }
2126
2127 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2128 assert(!incremental_collection_failed(), "Should have been cleared");
2129 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2130 cmsSpace()->gc_epilogue();
2131 // Print stat counters
2132 NOT_PRODUCT(
2133 assert(_numObjectsAllocated == 0, "check");
2134 assert(_numWordsAllocated == 0, "check");
2135 log_develop_trace(gc, promotion)("Promoted " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
2136 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2137 _numObjectsPromoted = 0;
2138 _numWordsPromoted = 0;
2139 )
2140
2141 // Call down the chain in contiguous_available needs the freelistLock
2142 // so print this out before releasing the freeListLock.
2143 log_develop_trace(gc)(" Contiguous available " SIZE_FORMAT " bytes ", contiguous_available());
2144 }
2145
2146 #ifndef PRODUCT
2147 bool CMSCollector::have_cms_token() {
2148 Thread* thr = Thread::current();
2149 if (thr->is_VM_thread()) {
2150 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2151 } else if (thr->is_ConcurrentGC_thread()) {
2152 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2153 } else if (thr->is_GC_task_thread()) {
2154 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2155 ParGCRareEvent_lock->owned_by_self();
2156 }
2157 return false;
2158 }
2159
2160 // Check reachability of the given heap address in CMS generation,
2161 // treating all other generations as roots.
2162 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2163 // We could "guarantee" below, rather than assert, but I'll
2164 // leave these as "asserts" so that an adventurous debugger
2165 // could try this in the product build provided some subset of
2166 // the conditions were met, provided they were interested in the
2167 // results and knew that the computation below wouldn't interfere
2168 // with other concurrent computations mutating the structures
2169 // being read or written.
2170 assert(SafepointSynchronize::is_at_safepoint(),
2171 "Else mutations in object graph will make answer suspect");
2172 assert(have_cms_token(), "Should hold cms token");
2173 assert(haveFreelistLocks(), "must hold free list locks");
2174 assert_lock_strong(bitMapLock());
2175
2176 // Clear the marking bit map array before starting, but, just
2177 // for kicks, first report if the given address is already marked
2178 tty->print_cr("Start: Address " PTR_FORMAT " is%s marked", p2i(addr),
2179 _markBitMap.isMarked(addr) ? "" : " not");
2180
2181 if (verify_after_remark()) {
2182 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2183 bool result = verification_mark_bm()->isMarked(addr);
2184 tty->print_cr("TransitiveMark: Address " PTR_FORMAT " %s marked", p2i(addr),
2185 result ? "IS" : "is NOT");
2186 return result;
2187 } else {
2188 tty->print_cr("Could not compute result");
2189 return false;
2190 }
2191 }
2192 #endif
2193
2194 void
2195 CMSCollector::print_on_error(outputStream* st) {
2196 CMSCollector* collector = ConcurrentMarkSweepGeneration::_collector;
2197 if (collector != NULL) {
2198 CMSBitMap* bitmap = &collector->_markBitMap;
2199 st->print_cr("Marking Bits: (CMSBitMap*) " PTR_FORMAT, p2i(bitmap));
2200 bitmap->print_on_error(st, " Bits: ");
2201
2202 st->cr();
2203
2204 CMSBitMap* mut_bitmap = &collector->_modUnionTable;
2205 st->print_cr("Mod Union Table: (CMSBitMap*) " PTR_FORMAT, p2i(mut_bitmap));
2206 mut_bitmap->print_on_error(st, " Bits: ");
2207 }
2208 }
2209
2210 ////////////////////////////////////////////////////////
2211 // CMS Verification Support
2212 ////////////////////////////////////////////////////////
2213 // Following the remark phase, the following invariant
2214 // should hold -- each object in the CMS heap which is
2215 // marked in markBitMap() should be marked in the verification_mark_bm().
2216
2217 class VerifyMarkedClosure: public BitMapClosure {
2218 CMSBitMap* _marks;
2219 bool _failed;
2220
2221 public:
2222 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2223
2224 bool do_bit(size_t offset) {
2225 HeapWord* addr = _marks->offsetToHeapWord(offset);
2226 if (!_marks->isMarked(addr)) {
2227 Log(gc, verify) log;
2228 ResourceMark rm;
2229 oop(addr)->print_on(log.error_stream());
2230 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
2231 _failed = true;
2232 }
2233 return true;
2234 }
2235
2236 bool failed() { return _failed; }
2237 };
2238
2239 bool CMSCollector::verify_after_remark() {
2240 GCTraceTime(Info, gc, phases, verify) tm("Verifying CMS Marking.");
2241 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2242 static bool init = false;
2243
2244 assert(SafepointSynchronize::is_at_safepoint(),
2245 "Else mutations in object graph will make answer suspect");
2246 assert(have_cms_token(),
2247 "Else there may be mutual interference in use of "
2248 " verification data structures");
2249 assert(_collectorState > Marking && _collectorState <= Sweeping,
2250 "Else marking info checked here may be obsolete");
2251 assert(haveFreelistLocks(), "must hold free list locks");
2252 assert_lock_strong(bitMapLock());
2253
2254
2255 // Allocate marking bit map if not already allocated
2256 if (!init) { // first time
2257 if (!verification_mark_bm()->allocate(_span)) {
2258 return false;
2259 }
2260 init = true;
2261 }
2262
2263 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2264
2265 // Turn off refs discovery -- so we will be tracing through refs.
2266 // This is as intended, because by this time
2267 // GC must already have cleared any refs that need to be cleared,
2268 // and traced those that need to be marked; moreover,
2269 // the marking done here is not going to interfere in any
2270 // way with the marking information used by GC.
2271 NoRefDiscovery no_discovery(ref_processor());
2272
2273 #if defined(COMPILER2) || INCLUDE_JVMCI
2274 DerivedPointerTableDeactivate dpt_deact;
2275 #endif
2276
2277 // Clear any marks from a previous round
2278 verification_mark_bm()->clear_all();
2279 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2280 verify_work_stacks_empty();
2281
2282 GenCollectedHeap* gch = GenCollectedHeap::heap();
2283 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2284 // Update the saved marks which may affect the root scans.
2285 gch->save_marks();
2286
2287 if (CMSRemarkVerifyVariant == 1) {
2288 // In this first variant of verification, we complete
2289 // all marking, then check if the new marks-vector is
2290 // a subset of the CMS marks-vector.
2291 verify_after_remark_work_1();
2292 } else {
2293 guarantee(CMSRemarkVerifyVariant == 2, "Range checking for CMSRemarkVerifyVariant should guarantee 1 or 2");
2294 // In this second variant of verification, we flag an error
2295 // (i.e. an object reachable in the new marks-vector not reachable
2296 // in the CMS marks-vector) immediately, also indicating the
2297 // identify of an object (A) that references the unmarked object (B) --
2298 // presumably, a mutation to A failed to be picked up by preclean/remark?
2299 verify_after_remark_work_2();
2300 }
2301
2302 return true;
2303 }
2304
2305 void CMSCollector::verify_after_remark_work_1() {
2306 ResourceMark rm;
2307 HandleMark hm;
2308 GenCollectedHeap* gch = GenCollectedHeap::heap();
2309
2310 // Get a clear set of claim bits for the roots processing to work with.
2311 ClassLoaderDataGraph::clear_claimed_marks();
2312
2313 // Mark from roots one level into CMS
2314 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2315 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2316
2317 {
2318 StrongRootsScope srs(1);
2319
2320 gch->gen_process_roots(&srs,
2321 GenCollectedHeap::OldGen,
2322 true, // young gen as roots
2323 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2324 should_unload_classes(),
2325 ¬Older,
2326 NULL,
2327 NULL);
2328 }
2329
2330 // Now mark from the roots
2331 MarkFromRootsClosure markFromRootsClosure(this, _span,
2332 verification_mark_bm(), verification_mark_stack(),
2333 false /* don't yield */, true /* verifying */);
2334 assert(_restart_addr == NULL, "Expected pre-condition");
2335 verification_mark_bm()->iterate(&markFromRootsClosure);
2336 while (_restart_addr != NULL) {
2337 // Deal with stack overflow: by restarting at the indicated
2338 // address.
2339 HeapWord* ra = _restart_addr;
2340 markFromRootsClosure.reset(ra);
2341 _restart_addr = NULL;
2342 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2343 }
2344 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2345 verify_work_stacks_empty();
2346
2347 // Marking completed -- now verify that each bit marked in
2348 // verification_mark_bm() is also marked in markBitMap(); flag all
2349 // errors by printing corresponding objects.
2350 VerifyMarkedClosure vcl(markBitMap());
2351 verification_mark_bm()->iterate(&vcl);
2352 if (vcl.failed()) {
2353 Log(gc, verify) log;
2354 log.error("Failed marking verification after remark");
2355 ResourceMark rm;
2356 gch->print_on(log.error_stream());
2357 fatal("CMS: failed marking verification after remark");
2358 }
2359 }
2360
2361 class VerifyKlassOopsKlassClosure : public KlassClosure {
2362 class VerifyKlassOopsClosure : public OopClosure {
2363 CMSBitMap* _bitmap;
2364 public:
2365 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2366 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2367 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2368 } _oop_closure;
2369 public:
2370 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2371 void do_klass(Klass* k) {
2372 k->oops_do(&_oop_closure);
2373 }
2374 };
2375
2376 void CMSCollector::verify_after_remark_work_2() {
2377 ResourceMark rm;
2378 HandleMark hm;
2379 GenCollectedHeap* gch = GenCollectedHeap::heap();
2380
2381 // Get a clear set of claim bits for the roots processing to work with.
2382 ClassLoaderDataGraph::clear_claimed_marks();
2383
2384 // Mark from roots one level into CMS
2385 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2386 markBitMap());
2387 CLDToOopClosure cld_closure(¬Older, true);
2388
2389 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2390
2391 {
2392 StrongRootsScope srs(1);
2393
2394 gch->gen_process_roots(&srs,
2395 GenCollectedHeap::OldGen,
2396 true, // young gen as roots
2397 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2398 should_unload_classes(),
2399 ¬Older,
2400 NULL,
2401 &cld_closure);
2402 }
2403
2404 // Now mark from the roots
2405 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2406 verification_mark_bm(), markBitMap(), verification_mark_stack());
2407 assert(_restart_addr == NULL, "Expected pre-condition");
2408 verification_mark_bm()->iterate(&markFromRootsClosure);
2409 while (_restart_addr != NULL) {
2410 // Deal with stack overflow: by restarting at the indicated
2411 // address.
2412 HeapWord* ra = _restart_addr;
2413 markFromRootsClosure.reset(ra);
2414 _restart_addr = NULL;
2415 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2416 }
2417 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2418 verify_work_stacks_empty();
2419
2420 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2421 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2422
2423 // Marking completed -- now verify that each bit marked in
2424 // verification_mark_bm() is also marked in markBitMap(); flag all
2425 // errors by printing corresponding objects.
2426 VerifyMarkedClosure vcl(markBitMap());
2427 verification_mark_bm()->iterate(&vcl);
2428 assert(!vcl.failed(), "Else verification above should not have succeeded");
2429 }
2430
2431 void ConcurrentMarkSweepGeneration::save_marks() {
2432 // delegate to CMS space
2433 cmsSpace()->save_marks();
2434 for (uint i = 0; i < ParallelGCThreads; i++) {
2435 _par_gc_thread_states[i]->promo.startTrackingPromotions();
2436 }
2437 }
2438
2439 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
2440 return cmsSpace()->no_allocs_since_save_marks();
2441 }
2442
2443 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
2444 \
2445 void ConcurrentMarkSweepGeneration:: \
2446 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
2447 cl->set_generation(this); \
2448 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
2449 cl->reset_generation(); \
2450 save_marks(); \
2451 }
2452
2453 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
2454
2455 void
2456 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
2457 if (freelistLock()->owned_by_self()) {
2458 Generation::oop_iterate(cl);
2459 } else {
2460 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2461 Generation::oop_iterate(cl);
2462 }
2463 }
2464
2465 void
2466 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
2467 if (freelistLock()->owned_by_self()) {
2468 Generation::object_iterate(cl);
2469 } else {
2470 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2471 Generation::object_iterate(cl);
2472 }
2473 }
2474
2475 void
2476 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
2477 if (freelistLock()->owned_by_self()) {
2478 Generation::safe_object_iterate(cl);
2479 } else {
2480 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2481 Generation::safe_object_iterate(cl);
2482 }
2483 }
2484
2485 void
2486 ConcurrentMarkSweepGeneration::post_compact() {
2487 }
2488
2489 void
2490 ConcurrentMarkSweepGeneration::prepare_for_verify() {
2491 // Fix the linear allocation blocks to look like free blocks.
2492
2493 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2494 // are not called when the heap is verified during universe initialization and
2495 // at vm shutdown.
2496 if (freelistLock()->owned_by_self()) {
2497 cmsSpace()->prepare_for_verify();
2498 } else {
2499 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2500 cmsSpace()->prepare_for_verify();
2501 }
2502 }
2503
2504 void
2505 ConcurrentMarkSweepGeneration::verify() {
2506 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
2507 // are not called when the heap is verified during universe initialization and
2508 // at vm shutdown.
2509 if (freelistLock()->owned_by_self()) {
2510 cmsSpace()->verify();
2511 } else {
2512 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
2513 cmsSpace()->verify();
2514 }
2515 }
2516
2517 void CMSCollector::verify() {
2518 _cmsGen->verify();
2519 }
2520
2521 #ifndef PRODUCT
2522 bool CMSCollector::overflow_list_is_empty() const {
2523 assert(_num_par_pushes >= 0, "Inconsistency");
2524 if (_overflow_list == NULL) {
2525 assert(_num_par_pushes == 0, "Inconsistency");
2526 }
2527 return _overflow_list == NULL;
2528 }
2529
2530 // The methods verify_work_stacks_empty() and verify_overflow_empty()
2531 // merely consolidate assertion checks that appear to occur together frequently.
2532 void CMSCollector::verify_work_stacks_empty() const {
2533 assert(_markStack.isEmpty(), "Marking stack should be empty");
2534 assert(overflow_list_is_empty(), "Overflow list should be empty");
2535 }
2536
2537 void CMSCollector::verify_overflow_empty() const {
2538 assert(overflow_list_is_empty(), "Overflow list should be empty");
2539 assert(no_preserved_marks(), "No preserved marks");
2540 }
2541 #endif // PRODUCT
2542
2543 // Decide if we want to enable class unloading as part of the
2544 // ensuing concurrent GC cycle. We will collect and
2545 // unload classes if it's the case that:
2546 // (1) an explicit gc request has been made and the flag
2547 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
2548 // (2) (a) class unloading is enabled at the command line, and
2549 // (b) old gen is getting really full
2550 // NOTE: Provided there is no change in the state of the heap between
2551 // calls to this method, it should have idempotent results. Moreover,
2552 // its results should be monotonically increasing (i.e. going from 0 to 1,
2553 // but not 1 to 0) between successive calls between which the heap was
2554 // not collected. For the implementation below, it must thus rely on
2555 // the property that concurrent_cycles_since_last_unload()
2556 // will not decrease unless a collection cycle happened and that
2557 // _cmsGen->is_too_full() are
2558 // themselves also monotonic in that sense. See check_monotonicity()
2559 // below.
2560 void CMSCollector::update_should_unload_classes() {
2561 _should_unload_classes = false;
2562 // Condition 1 above
2563 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
2564 _should_unload_classes = true;
2565 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
2566 // Disjuncts 2.b.(i,ii,iii) above
2567 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
2568 CMSClassUnloadingMaxInterval)
2569 || _cmsGen->is_too_full();
2570 }
2571 }
2572
2573 bool ConcurrentMarkSweepGeneration::is_too_full() const {
2574 bool res = should_concurrent_collect();
2575 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
2576 return res;
2577 }
2578
2579 void CMSCollector::setup_cms_unloading_and_verification_state() {
2580 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
2581 || VerifyBeforeExit;
2582 const int rso = GenCollectedHeap::SO_AllCodeCache;
2583
2584 // We set the proper root for this CMS cycle here.
2585 if (should_unload_classes()) { // Should unload classes this cycle
2586 remove_root_scanning_option(rso); // Shrink the root set appropriately
2587 set_verifying(should_verify); // Set verification state for this cycle
2588 return; // Nothing else needs to be done at this time
2589 }
2590
2591 // Not unloading classes this cycle
2592 assert(!should_unload_classes(), "Inconsistency!");
2593
2594 // If we are not unloading classes then add SO_AllCodeCache to root
2595 // scanning options.
2596 add_root_scanning_option(rso);
2597
2598 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
2599 set_verifying(true);
2600 } else if (verifying() && !should_verify) {
2601 // We were verifying, but some verification flags got disabled.
2602 set_verifying(false);
2603 // Exclude symbols, strings and code cache elements from root scanning to
2604 // reduce IM and RM pauses.
2605 remove_root_scanning_option(rso);
2606 }
2607 }
2608
2609
2610 #ifndef PRODUCT
2611 HeapWord* CMSCollector::block_start(const void* p) const {
2612 const HeapWord* addr = (HeapWord*)p;
2613 if (_span.contains(p)) {
2614 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
2615 return _cmsGen->cmsSpace()->block_start(p);
2616 }
2617 }
2618 return NULL;
2619 }
2620 #endif
2621
2622 HeapWord*
2623 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
2624 bool tlab,
2625 bool parallel) {
2626 CMSSynchronousYieldRequest yr;
2627 assert(!tlab, "Can't deal with TLAB allocation");
2628 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
2629 expand_for_gc_cause(word_size*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_satisfy_allocation);
2630 if (GCExpandToAllocateDelayMillis > 0) {
2631 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2632 }
2633 return have_lock_and_allocate(word_size, tlab);
2634 }
2635
2636 void ConcurrentMarkSweepGeneration::expand_for_gc_cause(
2637 size_t bytes,
2638 size_t expand_bytes,
2639 CMSExpansionCause::Cause cause)
2640 {
2641
2642 bool success = expand(bytes, expand_bytes);
2643
2644 // remember why we expanded; this information is used
2645 // by shouldConcurrentCollect() when making decisions on whether to start
2646 // a new CMS cycle.
2647 if (success) {
2648 set_expansion_cause(cause);
2649 log_trace(gc)("Expanded CMS gen for %s", CMSExpansionCause::to_string(cause));
2650 }
2651 }
2652
2653 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
2654 HeapWord* res = NULL;
2655 MutexLocker x(ParGCRareEvent_lock);
2656 while (true) {
2657 // Expansion by some other thread might make alloc OK now:
2658 res = ps->lab.alloc(word_sz);
2659 if (res != NULL) return res;
2660 // If there's not enough expansion space available, give up.
2661 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
2662 return NULL;
2663 }
2664 // Otherwise, we try expansion.
2665 expand_for_gc_cause(word_sz*HeapWordSize, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_lab);
2666 // Now go around the loop and try alloc again;
2667 // A competing par_promote might beat us to the expansion space,
2668 // so we may go around the loop again if promotion fails again.
2669 if (GCExpandToAllocateDelayMillis > 0) {
2670 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2671 }
2672 }
2673 }
2674
2675
2676 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
2677 PromotionInfo* promo) {
2678 MutexLocker x(ParGCRareEvent_lock);
2679 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
2680 while (true) {
2681 // Expansion by some other thread might make alloc OK now:
2682 if (promo->ensure_spooling_space()) {
2683 assert(promo->has_spooling_space(),
2684 "Post-condition of successful ensure_spooling_space()");
2685 return true;
2686 }
2687 // If there's not enough expansion space available, give up.
2688 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
2689 return false;
2690 }
2691 // Otherwise, we try expansion.
2692 expand_for_gc_cause(refill_size_bytes, MinHeapDeltaBytes, CMSExpansionCause::_allocate_par_spooling_space);
2693 // Now go around the loop and try alloc again;
2694 // A competing allocation might beat us to the expansion space,
2695 // so we may go around the loop again if allocation fails again.
2696 if (GCExpandToAllocateDelayMillis > 0) {
2697 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
2698 }
2699 }
2700 }
2701
2702 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
2703 // Only shrink if a compaction was done so that all the free space
2704 // in the generation is in a contiguous block at the end.
2705 if (did_compact()) {
2706 CardGeneration::shrink(bytes);
2707 }
2708 }
2709
2710 void ConcurrentMarkSweepGeneration::assert_correct_size_change_locking() {
2711 assert_locked_or_safepoint(Heap_lock);
2712 }
2713
2714 void ConcurrentMarkSweepGeneration::shrink_free_list_by(size_t bytes) {
2715 assert_locked_or_safepoint(Heap_lock);
2716 assert_lock_strong(freelistLock());
2717 log_trace(gc)("Shrinking of CMS not yet implemented");
2718 return;
2719 }
2720
2721
2722 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
2723 // phases.
2724 class CMSPhaseAccounting: public StackObj {
2725 public:
2726 CMSPhaseAccounting(CMSCollector *collector,
2727 const char *title);
2728 ~CMSPhaseAccounting();
2729
2730 private:
2731 CMSCollector *_collector;
2732 const char *_title;
2733 GCTraceConcTime(Info, gc) _trace_time;
2734
2735 public:
2736 // Not MT-safe; so do not pass around these StackObj's
2737 // where they may be accessed by other threads.
2738 double wallclock_millis() {
2739 return TimeHelper::counter_to_millis(os::elapsed_counter() - _trace_time.start_time());
2740 }
2741 };
2742
2743 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
2744 const char *title) :
2745 _collector(collector), _title(title), _trace_time(title) {
2746
2747 _collector->resetYields();
2748 _collector->resetTimer();
2749 _collector->startTimer();
2750 _collector->gc_timer_cm()->register_gc_concurrent_start(title);
2751 }
2752
2753 CMSPhaseAccounting::~CMSPhaseAccounting() {
2754 _collector->gc_timer_cm()->register_gc_concurrent_end();
2755 _collector->stopTimer();
2756 log_debug(gc)("Concurrent active time: %.3fms", TimeHelper::counter_to_seconds(_collector->timerTicks()));
2757 log_trace(gc)(" (CMS %s yielded %d times)", _title, _collector->yields());
2758 }
2759
2760 // CMS work
2761
2762 // The common parts of CMSParInitialMarkTask and CMSParRemarkTask.
2763 class CMSParMarkTask : public AbstractGangTask {
2764 protected:
2765 CMSCollector* _collector;
2766 uint _n_workers;
2767 CMSParMarkTask(const char* name, CMSCollector* collector, uint n_workers) :
2768 AbstractGangTask(name),
2769 _collector(collector),
2770 _n_workers(n_workers) {}
2771 // Work method in support of parallel rescan ... of young gen spaces
2772 void do_young_space_rescan(OopsInGenClosure* cl,
2773 ContiguousSpace* space,
2774 HeapWord** chunk_array, size_t chunk_top);
2775 void work_on_young_gen_roots(OopsInGenClosure* cl);
2776 };
2777
2778 // Parallel initial mark task
2779 class CMSParInitialMarkTask: public CMSParMarkTask {
2780 StrongRootsScope* _strong_roots_scope;
2781 public:
2782 CMSParInitialMarkTask(CMSCollector* collector, StrongRootsScope* strong_roots_scope, uint n_workers) :
2783 CMSParMarkTask("Scan roots and young gen for initial mark in parallel", collector, n_workers),
2784 _strong_roots_scope(strong_roots_scope) {}
2785 void work(uint worker_id);
2786 };
2787
2788 // Checkpoint the roots into this generation from outside
2789 // this generation. [Note this initial checkpoint need only
2790 // be approximate -- we'll do a catch up phase subsequently.]
2791 void CMSCollector::checkpointRootsInitial() {
2792 assert(_collectorState == InitialMarking, "Wrong collector state");
2793 check_correct_thread_executing();
2794 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
2795
2796 save_heap_summary();
2797 report_heap_summary(GCWhen::BeforeGC);
2798
2799 ReferenceProcessor* rp = ref_processor();
2800 assert(_restart_addr == NULL, "Control point invariant");
2801 {
2802 // acquire locks for subsequent manipulations
2803 MutexLockerEx x(bitMapLock(),
2804 Mutex::_no_safepoint_check_flag);
2805 checkpointRootsInitialWork();
2806 // enable ("weak") refs discovery
2807 rp->enable_discovery();
2808 _collectorState = Marking;
2809 }
2810 }
2811
2812 void CMSCollector::checkpointRootsInitialWork() {
2813 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
2814 assert(_collectorState == InitialMarking, "just checking");
2815
2816 // Already have locks.
2817 assert_lock_strong(bitMapLock());
2818 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
2819
2820 // Setup the verification and class unloading state for this
2821 // CMS collection cycle.
2822 setup_cms_unloading_and_verification_state();
2823
2824 GCTraceTime(Trace, gc, phases) ts("checkpointRootsInitialWork", _gc_timer_cm);
2825
2826 // Reset all the PLAB chunk arrays if necessary.
2827 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
2828 reset_survivor_plab_arrays();
2829 }
2830
2831 ResourceMark rm;
2832 HandleMark hm;
2833
2834 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
2835 GenCollectedHeap* gch = GenCollectedHeap::heap();
2836
2837 verify_work_stacks_empty();
2838 verify_overflow_empty();
2839
2840 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2841 // Update the saved marks which may affect the root scans.
2842 gch->save_marks();
2843
2844 // weak reference processing has not started yet.
2845 ref_processor()->set_enqueuing_is_done(false);
2846
2847 // Need to remember all newly created CLDs,
2848 // so that we can guarantee that the remark finds them.
2849 ClassLoaderDataGraph::remember_new_clds(true);
2850
2851 // Whenever a CLD is found, it will be claimed before proceeding to mark
2852 // the klasses. The claimed marks need to be cleared before marking starts.
2853 ClassLoaderDataGraph::clear_claimed_marks();
2854
2855 print_eden_and_survivor_chunk_arrays();
2856
2857 {
2858 #if defined(COMPILER2) || INCLUDE_JVMCI
2859 DerivedPointerTableDeactivate dpt_deact;
2860 #endif
2861 if (CMSParallelInitialMarkEnabled) {
2862 // The parallel version.
2863 WorkGang* workers = gch->workers();
2864 assert(workers != NULL, "Need parallel worker threads.");
2865 uint n_workers = workers->active_workers();
2866
2867 StrongRootsScope srs(n_workers);
2868
2869 CMSParInitialMarkTask tsk(this, &srs, n_workers);
2870 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
2871 if (n_workers > 1) {
2872 workers->run_task(&tsk);
2873 } else {
2874 tsk.work(0);
2875 }
2876 } else {
2877 // The serial version.
2878 CLDToOopClosure cld_closure(¬Older, true);
2879 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2880
2881 StrongRootsScope srs(1);
2882
2883 gch->gen_process_roots(&srs,
2884 GenCollectedHeap::OldGen,
2885 true, // young gen as roots
2886 GenCollectedHeap::ScanningOption(roots_scanning_options()),
2887 should_unload_classes(),
2888 ¬Older,
2889 NULL,
2890 &cld_closure);
2891 }
2892 }
2893
2894 // Clear mod-union table; it will be dirtied in the prologue of
2895 // CMS generation per each young generation collection.
2896
2897 assert(_modUnionTable.isAllClear(),
2898 "Was cleared in most recent final checkpoint phase"
2899 " or no bits are set in the gc_prologue before the start of the next "
2900 "subsequent marking phase.");
2901
2902 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
2903
2904 // Save the end of the used_region of the constituent generations
2905 // to be used to limit the extent of sweep in each generation.
2906 save_sweep_limits();
2907 verify_overflow_empty();
2908 }
2909
2910 bool CMSCollector::markFromRoots() {
2911 // we might be tempted to assert that:
2912 // assert(!SafepointSynchronize::is_at_safepoint(),
2913 // "inconsistent argument?");
2914 // However that wouldn't be right, because it's possible that
2915 // a safepoint is indeed in progress as a young generation
2916 // stop-the-world GC happens even as we mark in this generation.
2917 assert(_collectorState == Marking, "inconsistent state?");
2918 check_correct_thread_executing();
2919 verify_overflow_empty();
2920
2921 // Weak ref discovery note: We may be discovering weak
2922 // refs in this generation concurrent (but interleaved) with
2923 // weak ref discovery by the young generation collector.
2924
2925 CMSTokenSyncWithLocks ts(true, bitMapLock());
2926 GCTraceCPUTime tcpu;
2927 CMSPhaseAccounting pa(this, "Concurrent Mark");
2928 bool res = markFromRootsWork();
2929 if (res) {
2930 _collectorState = Precleaning;
2931 } else { // We failed and a foreground collection wants to take over
2932 assert(_foregroundGCIsActive, "internal state inconsistency");
2933 assert(_restart_addr == NULL, "foreground will restart from scratch");
2934 log_debug(gc)("bailing out to foreground collection");
2935 }
2936 verify_overflow_empty();
2937 return res;
2938 }
2939
2940 bool CMSCollector::markFromRootsWork() {
2941 // iterate over marked bits in bit map, doing a full scan and mark
2942 // from these roots using the following algorithm:
2943 // . if oop is to the right of the current scan pointer,
2944 // mark corresponding bit (we'll process it later)
2945 // . else (oop is to left of current scan pointer)
2946 // push oop on marking stack
2947 // . drain the marking stack
2948
2949 // Note that when we do a marking step we need to hold the
2950 // bit map lock -- recall that direct allocation (by mutators)
2951 // and promotion (by the young generation collector) is also
2952 // marking the bit map. [the so-called allocate live policy.]
2953 // Because the implementation of bit map marking is not
2954 // robust wrt simultaneous marking of bits in the same word,
2955 // we need to make sure that there is no such interference
2956 // between concurrent such updates.
2957
2958 // already have locks
2959 assert_lock_strong(bitMapLock());
2960
2961 verify_work_stacks_empty();
2962 verify_overflow_empty();
2963 bool result = false;
2964 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
2965 result = do_marking_mt();
2966 } else {
2967 result = do_marking_st();
2968 }
2969 return result;
2970 }
2971
2972 // Forward decl
2973 class CMSConcMarkingTask;
2974
2975 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
2976 CMSCollector* _collector;
2977 CMSConcMarkingTask* _task;
2978 public:
2979 virtual void yield();
2980
2981 // "n_threads" is the number of threads to be terminated.
2982 // "queue_set" is a set of work queues of other threads.
2983 // "collector" is the CMS collector associated with this task terminator.
2984 // "yield" indicates whether we need the gang as a whole to yield.
2985 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
2986 ParallelTaskTerminator(n_threads, queue_set),
2987 _collector(collector) { }
2988
2989 void set_task(CMSConcMarkingTask* task) {
2990 _task = task;
2991 }
2992 };
2993
2994 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
2995 CMSConcMarkingTask* _task;
2996 public:
2997 bool should_exit_termination();
2998 void set_task(CMSConcMarkingTask* task) {
2999 _task = task;
3000 }
3001 };
3002
3003 // MT Concurrent Marking Task
3004 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3005 CMSCollector* _collector;
3006 uint _n_workers; // requested/desired # workers
3007 bool _result;
3008 CompactibleFreeListSpace* _cms_space;
3009 char _pad_front[64]; // padding to ...
3010 HeapWord* _global_finger; // ... avoid sharing cache line
3011 char _pad_back[64];
3012 HeapWord* _restart_addr;
3013
3014 // Exposed here for yielding support
3015 Mutex* const _bit_map_lock;
3016
3017 // The per thread work queues, available here for stealing
3018 OopTaskQueueSet* _task_queues;
3019
3020 // Termination (and yielding) support
3021 CMSConcMarkingTerminator _term;
3022 CMSConcMarkingTerminatorTerminator _term_term;
3023
3024 public:
3025 CMSConcMarkingTask(CMSCollector* collector,
3026 CompactibleFreeListSpace* cms_space,
3027 YieldingFlexibleWorkGang* workers,
3028 OopTaskQueueSet* task_queues):
3029 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3030 _collector(collector),
3031 _cms_space(cms_space),
3032 _n_workers(0), _result(true),
3033 _task_queues(task_queues),
3034 _term(_n_workers, task_queues, _collector),
3035 _bit_map_lock(collector->bitMapLock())
3036 {
3037 _requested_size = _n_workers;
3038 _term.set_task(this);
3039 _term_term.set_task(this);
3040 _restart_addr = _global_finger = _cms_space->bottom();
3041 }
3042
3043
3044 OopTaskQueueSet* task_queues() { return _task_queues; }
3045
3046 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3047
3048 HeapWord** global_finger_addr() { return &_global_finger; }
3049
3050 CMSConcMarkingTerminator* terminator() { return &_term; }
3051
3052 virtual void set_for_termination(uint active_workers) {
3053 terminator()->reset_for_reuse(active_workers);
3054 }
3055
3056 void work(uint worker_id);
3057 bool should_yield() {
3058 return ConcurrentMarkSweepThread::should_yield()
3059 && !_collector->foregroundGCIsActive();
3060 }
3061
3062 virtual void coordinator_yield(); // stuff done by coordinator
3063 bool result() { return _result; }
3064
3065 void reset(HeapWord* ra) {
3066 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3067 _restart_addr = _global_finger = ra;
3068 _term.reset_for_reuse();
3069 }
3070
3071 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3072 OopTaskQueue* work_q);
3073
3074 private:
3075 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3076 void do_work_steal(int i);
3077 void bump_global_finger(HeapWord* f);
3078 };
3079
3080 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3081 assert(_task != NULL, "Error");
3082 return _task->yielding();
3083 // Note that we do not need the disjunct || _task->should_yield() above
3084 // because we want terminating threads to yield only if the task
3085 // is already in the midst of yielding, which happens only after at least one
3086 // thread has yielded.
3087 }
3088
3089 void CMSConcMarkingTerminator::yield() {
3090 if (_task->should_yield()) {
3091 _task->yield();
3092 } else {
3093 ParallelTaskTerminator::yield();
3094 }
3095 }
3096
3097 ////////////////////////////////////////////////////////////////
3098 // Concurrent Marking Algorithm Sketch
3099 ////////////////////////////////////////////////////////////////
3100 // Until all tasks exhausted (both spaces):
3101 // -- claim next available chunk
3102 // -- bump global finger via CAS
3103 // -- find first object that starts in this chunk
3104 // and start scanning bitmap from that position
3105 // -- scan marked objects for oops
3106 // -- CAS-mark target, and if successful:
3107 // . if target oop is above global finger (volatile read)
3108 // nothing to do
3109 // . if target oop is in chunk and above local finger
3110 // then nothing to do
3111 // . else push on work-queue
3112 // -- Deal with possible overflow issues:
3113 // . local work-queue overflow causes stuff to be pushed on
3114 // global (common) overflow queue
3115 // . always first empty local work queue
3116 // . then get a batch of oops from global work queue if any
3117 // . then do work stealing
3118 // -- When all tasks claimed (both spaces)
3119 // and local work queue empty,
3120 // then in a loop do:
3121 // . check global overflow stack; steal a batch of oops and trace
3122 // . try to steal from other threads oif GOS is empty
3123 // . if neither is available, offer termination
3124 // -- Terminate and return result
3125 //
3126 void CMSConcMarkingTask::work(uint worker_id) {
3127 elapsedTimer _timer;
3128 ResourceMark rm;
3129 HandleMark hm;
3130
3131 DEBUG_ONLY(_collector->verify_overflow_empty();)
3132
3133 // Before we begin work, our work queue should be empty
3134 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3135 // Scan the bitmap covering _cms_space, tracing through grey objects.
3136 _timer.start();
3137 do_scan_and_mark(worker_id, _cms_space);
3138 _timer.stop();
3139 log_trace(gc, task)("Finished cms space scanning in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3140
3141 // ... do work stealing
3142 _timer.reset();
3143 _timer.start();
3144 do_work_steal(worker_id);
3145 _timer.stop();
3146 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
3147 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3148 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3149 // Note that under the current task protocol, the
3150 // following assertion is true even of the spaces
3151 // expanded since the completion of the concurrent
3152 // marking. XXX This will likely change under a strict
3153 // ABORT semantics.
3154 // After perm removal the comparison was changed to
3155 // greater than or equal to from strictly greater than.
3156 // Before perm removal the highest address sweep would
3157 // have been at the end of perm gen but now is at the
3158 // end of the tenured gen.
3159 assert(_global_finger >= _cms_space->end(),
3160 "All tasks have been completed");
3161 DEBUG_ONLY(_collector->verify_overflow_empty();)
3162 }
3163
3164 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3165 HeapWord* read = _global_finger;
3166 HeapWord* cur = read;
3167 while (f > read) {
3168 cur = read;
3169 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3170 if (cur == read) {
3171 // our cas succeeded
3172 assert(_global_finger >= f, "protocol consistency");
3173 break;
3174 }
3175 }
3176 }
3177
3178 // This is really inefficient, and should be redone by
3179 // using (not yet available) block-read and -write interfaces to the
3180 // stack and the work_queue. XXX FIX ME !!!
3181 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3182 OopTaskQueue* work_q) {
3183 // Fast lock-free check
3184 if (ovflw_stk->length() == 0) {
3185 return false;
3186 }
3187 assert(work_q->size() == 0, "Shouldn't steal");
3188 MutexLockerEx ml(ovflw_stk->par_lock(),
3189 Mutex::_no_safepoint_check_flag);
3190 // Grab up to 1/4 the size of the work queue
3191 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3192 (size_t)ParGCDesiredObjsFromOverflowList);
3193 num = MIN2(num, ovflw_stk->length());
3194 for (int i = (int) num; i > 0; i--) {
3195 oop cur = ovflw_stk->pop();
3196 assert(cur != NULL, "Counted wrong?");
3197 work_q->push(cur);
3198 }
3199 return num > 0;
3200 }
3201
3202 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3203 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3204 int n_tasks = pst->n_tasks();
3205 // We allow that there may be no tasks to do here because
3206 // we are restarting after a stack overflow.
3207 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3208 uint nth_task = 0;
3209
3210 HeapWord* aligned_start = sp->bottom();
3211 if (sp->used_region().contains(_restart_addr)) {
3212 // Align down to a card boundary for the start of 0th task
3213 // for this space.
3214 aligned_start =
3215 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3216 CardTableModRefBS::card_size);
3217 }
3218
3219 size_t chunk_size = sp->marking_task_size();
3220 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3221 // Having claimed the nth task in this space,
3222 // compute the chunk that it corresponds to:
3223 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3224 aligned_start + (nth_task+1)*chunk_size);
3225 // Try and bump the global finger via a CAS;
3226 // note that we need to do the global finger bump
3227 // _before_ taking the intersection below, because
3228 // the task corresponding to that region will be
3229 // deemed done even if the used_region() expands
3230 // because of allocation -- as it almost certainly will
3231 // during start-up while the threads yield in the
3232 // closure below.
3233 HeapWord* finger = span.end();
3234 bump_global_finger(finger); // atomically
3235 // There are null tasks here corresponding to chunks
3236 // beyond the "top" address of the space.
3237 span = span.intersection(sp->used_region());
3238 if (!span.is_empty()) { // Non-null task
3239 HeapWord* prev_obj;
3240 assert(!span.contains(_restart_addr) || nth_task == 0,
3241 "Inconsistency");
3242 if (nth_task == 0) {
3243 // For the 0th task, we'll not need to compute a block_start.
3244 if (span.contains(_restart_addr)) {
3245 // In the case of a restart because of stack overflow,
3246 // we might additionally skip a chunk prefix.
3247 prev_obj = _restart_addr;
3248 } else {
3249 prev_obj = span.start();
3250 }
3251 } else {
3252 // We want to skip the first object because
3253 // the protocol is to scan any object in its entirety
3254 // that _starts_ in this span; a fortiori, any
3255 // object starting in an earlier span is scanned
3256 // as part of an earlier claimed task.
3257 // Below we use the "careful" version of block_start
3258 // so we do not try to navigate uninitialized objects.
3259 prev_obj = sp->block_start_careful(span.start());
3260 // Below we use a variant of block_size that uses the
3261 // Printezis bits to avoid waiting for allocated
3262 // objects to become initialized/parsable.
3263 while (prev_obj < span.start()) {
3264 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3265 if (sz > 0) {
3266 prev_obj += sz;
3267 } else {
3268 // In this case we may end up doing a bit of redundant
3269 // scanning, but that appears unavoidable, short of
3270 // locking the free list locks; see bug 6324141.
3271 break;
3272 }
3273 }
3274 }
3275 if (prev_obj < span.end()) {
3276 MemRegion my_span = MemRegion(prev_obj, span.end());
3277 // Do the marking work within a non-empty span --
3278 // the last argument to the constructor indicates whether the
3279 // iteration should be incremental with periodic yields.
3280 ParMarkFromRootsClosure cl(this, _collector, my_span,
3281 &_collector->_markBitMap,
3282 work_queue(i),
3283 &_collector->_markStack);
3284 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
3285 } // else nothing to do for this task
3286 } // else nothing to do for this task
3287 }
3288 // We'd be tempted to assert here that since there are no
3289 // more tasks left to claim in this space, the global_finger
3290 // must exceed space->top() and a fortiori space->end(). However,
3291 // that would not quite be correct because the bumping of
3292 // global_finger occurs strictly after the claiming of a task,
3293 // so by the time we reach here the global finger may not yet
3294 // have been bumped up by the thread that claimed the last
3295 // task.
3296 pst->all_tasks_completed();
3297 }
3298
3299 class ParConcMarkingClosure: public MetadataAwareOopClosure {
3300 private:
3301 CMSCollector* _collector;
3302 CMSConcMarkingTask* _task;
3303 MemRegion _span;
3304 CMSBitMap* _bit_map;
3305 CMSMarkStack* _overflow_stack;
3306 OopTaskQueue* _work_queue;
3307 protected:
3308 DO_OOP_WORK_DEFN
3309 public:
3310 ParConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
3311 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
3312 MetadataAwareOopClosure(collector->ref_processor()),
3313 _collector(collector),
3314 _task(task),
3315 _span(collector->_span),
3316 _work_queue(work_queue),
3317 _bit_map(bit_map),
3318 _overflow_stack(overflow_stack)
3319 { }
3320 virtual void do_oop(oop* p);
3321 virtual void do_oop(narrowOop* p);
3322
3323 void trim_queue(size_t max);
3324 void handle_stack_overflow(HeapWord* lost);
3325 void do_yield_check() {
3326 if (_task->should_yield()) {
3327 _task->yield();
3328 }
3329 }
3330 };
3331
3332 DO_OOP_WORK_IMPL(ParConcMarkingClosure)
3333
3334 // Grey object scanning during work stealing phase --
3335 // the salient assumption here is that any references
3336 // that are in these stolen objects being scanned must
3337 // already have been initialized (else they would not have
3338 // been published), so we do not need to check for
3339 // uninitialized objects before pushing here.
3340 void ParConcMarkingClosure::do_oop(oop obj) {
3341 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
3342 HeapWord* addr = (HeapWord*)obj;
3343 // Check if oop points into the CMS generation
3344 // and is not marked
3345 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
3346 // a white object ...
3347 // If we manage to "claim" the object, by being the
3348 // first thread to mark it, then we push it on our
3349 // marking stack
3350 if (_bit_map->par_mark(addr)) { // ... now grey
3351 // push on work queue (grey set)
3352 bool simulate_overflow = false;
3353 NOT_PRODUCT(
3354 if (CMSMarkStackOverflowALot &&
3355 _collector->simulate_overflow()) {
3356 // simulate a stack overflow
3357 simulate_overflow = true;
3358 }
3359 )
3360 if (simulate_overflow ||
3361 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
3362 // stack overflow
3363 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
3364 // We cannot assert that the overflow stack is full because
3365 // it may have been emptied since.
3366 assert(simulate_overflow ||
3367 _work_queue->size() == _work_queue->max_elems(),
3368 "Else push should have succeeded");
3369 handle_stack_overflow(addr);
3370 }
3371 } // Else, some other thread got there first
3372 do_yield_check();
3373 }
3374 }
3375
3376 void ParConcMarkingClosure::do_oop(oop* p) { ParConcMarkingClosure::do_oop_work(p); }
3377 void ParConcMarkingClosure::do_oop(narrowOop* p) { ParConcMarkingClosure::do_oop_work(p); }
3378
3379 void ParConcMarkingClosure::trim_queue(size_t max) {
3380 while (_work_queue->size() > max) {
3381 oop new_oop;
3382 if (_work_queue->pop_local(new_oop)) {
3383 assert(new_oop->is_oop(), "Should be an oop");
3384 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
3385 assert(_span.contains((HeapWord*)new_oop), "Not in span");
3386 new_oop->oop_iterate(this); // do_oop() above
3387 do_yield_check();
3388 }
3389 }
3390 }
3391
3392 // Upon stack overflow, we discard (part of) the stack,
3393 // remembering the least address amongst those discarded
3394 // in CMSCollector's _restart_address.
3395 void ParConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
3396 // We need to do this under a mutex to prevent other
3397 // workers from interfering with the work done below.
3398 MutexLockerEx ml(_overflow_stack->par_lock(),
3399 Mutex::_no_safepoint_check_flag);
3400 // Remember the least grey address discarded
3401 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
3402 _collector->lower_restart_addr(ra);
3403 _overflow_stack->reset(); // discard stack contents
3404 _overflow_stack->expand(); // expand the stack if possible
3405 }
3406
3407
3408 void CMSConcMarkingTask::do_work_steal(int i) {
3409 OopTaskQueue* work_q = work_queue(i);
3410 oop obj_to_scan;
3411 CMSBitMap* bm = &(_collector->_markBitMap);
3412 CMSMarkStack* ovflw = &(_collector->_markStack);
3413 int* seed = _collector->hash_seed(i);
3414 ParConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
3415 while (true) {
3416 cl.trim_queue(0);
3417 assert(work_q->size() == 0, "Should have been emptied above");
3418 if (get_work_from_overflow_stack(ovflw, work_q)) {
3419 // Can't assert below because the work obtained from the
3420 // overflow stack may already have been stolen from us.
3421 // assert(work_q->size() > 0, "Work from overflow stack");
3422 continue;
3423 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
3424 assert(obj_to_scan->is_oop(), "Should be an oop");
3425 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
3426 obj_to_scan->oop_iterate(&cl);
3427 } else if (terminator()->offer_termination(&_term_term)) {
3428 assert(work_q->size() == 0, "Impossible!");
3429 break;
3430 } else if (yielding() || should_yield()) {
3431 yield();
3432 }
3433 }
3434 }
3435
3436 // This is run by the CMS (coordinator) thread.
3437 void CMSConcMarkingTask::coordinator_yield() {
3438 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3439 "CMS thread should hold CMS token");
3440 // First give up the locks, then yield, then re-lock
3441 // We should probably use a constructor/destructor idiom to
3442 // do this unlock/lock or modify the MutexUnlocker class to
3443 // serve our purpose. XXX
3444 assert_lock_strong(_bit_map_lock);
3445 _bit_map_lock->unlock();
3446 ConcurrentMarkSweepThread::desynchronize(true);
3447 _collector->stopTimer();
3448 _collector->incrementYields();
3449
3450 // It is possible for whichever thread initiated the yield request
3451 // not to get a chance to wake up and take the bitmap lock between
3452 // this thread releasing it and reacquiring it. So, while the
3453 // should_yield() flag is on, let's sleep for a bit to give the
3454 // other thread a chance to wake up. The limit imposed on the number
3455 // of iterations is defensive, to avoid any unforseen circumstances
3456 // putting us into an infinite loop. Since it's always been this
3457 // (coordinator_yield()) method that was observed to cause the
3458 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
3459 // which is by default non-zero. For the other seven methods that
3460 // also perform the yield operation, as are using a different
3461 // parameter (CMSYieldSleepCount) which is by default zero. This way we
3462 // can enable the sleeping for those methods too, if necessary.
3463 // See 6442774.
3464 //
3465 // We really need to reconsider the synchronization between the GC
3466 // thread and the yield-requesting threads in the future and we
3467 // should really use wait/notify, which is the recommended
3468 // way of doing this type of interaction. Additionally, we should
3469 // consolidate the eight methods that do the yield operation and they
3470 // are almost identical into one for better maintainability and
3471 // readability. See 6445193.
3472 //
3473 // Tony 2006.06.29
3474 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
3475 ConcurrentMarkSweepThread::should_yield() &&
3476 !CMSCollector::foregroundGCIsActive(); ++i) {
3477 os::sleep(Thread::current(), 1, false);
3478 }
3479
3480 ConcurrentMarkSweepThread::synchronize(true);
3481 _bit_map_lock->lock_without_safepoint_check();
3482 _collector->startTimer();
3483 }
3484
3485 bool CMSCollector::do_marking_mt() {
3486 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
3487 uint num_workers = AdaptiveSizePolicy::calc_active_conc_workers(conc_workers()->total_workers(),
3488 conc_workers()->active_workers(),
3489 Threads::number_of_non_daemon_threads());
3490 conc_workers()->set_active_workers(num_workers);
3491
3492 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
3493
3494 CMSConcMarkingTask tsk(this,
3495 cms_space,
3496 conc_workers(),
3497 task_queues());
3498
3499 // Since the actual number of workers we get may be different
3500 // from the number we requested above, do we need to do anything different
3501 // below? In particular, may be we need to subclass the SequantialSubTasksDone
3502 // class?? XXX
3503 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
3504
3505 // Refs discovery is already non-atomic.
3506 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
3507 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
3508 conc_workers()->start_task(&tsk);
3509 while (tsk.yielded()) {
3510 tsk.coordinator_yield();
3511 conc_workers()->continue_task(&tsk);
3512 }
3513 // If the task was aborted, _restart_addr will be non-NULL
3514 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
3515 while (_restart_addr != NULL) {
3516 // XXX For now we do not make use of ABORTED state and have not
3517 // yet implemented the right abort semantics (even in the original
3518 // single-threaded CMS case). That needs some more investigation
3519 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
3520 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
3521 // If _restart_addr is non-NULL, a marking stack overflow
3522 // occurred; we need to do a fresh marking iteration from the
3523 // indicated restart address.
3524 if (_foregroundGCIsActive) {
3525 // We may be running into repeated stack overflows, having
3526 // reached the limit of the stack size, while making very
3527 // slow forward progress. It may be best to bail out and
3528 // let the foreground collector do its job.
3529 // Clear _restart_addr, so that foreground GC
3530 // works from scratch. This avoids the headache of
3531 // a "rescan" which would otherwise be needed because
3532 // of the dirty mod union table & card table.
3533 _restart_addr = NULL;
3534 return false;
3535 }
3536 // Adjust the task to restart from _restart_addr
3537 tsk.reset(_restart_addr);
3538 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
3539 _restart_addr);
3540 _restart_addr = NULL;
3541 // Get the workers going again
3542 conc_workers()->start_task(&tsk);
3543 while (tsk.yielded()) {
3544 tsk.coordinator_yield();
3545 conc_workers()->continue_task(&tsk);
3546 }
3547 }
3548 assert(tsk.completed(), "Inconsistency");
3549 assert(tsk.result() == true, "Inconsistency");
3550 return true;
3551 }
3552
3553 bool CMSCollector::do_marking_st() {
3554 ResourceMark rm;
3555 HandleMark hm;
3556
3557 // Temporarily make refs discovery single threaded (non-MT)
3558 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
3559 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
3560 &_markStack, CMSYield);
3561 // the last argument to iterate indicates whether the iteration
3562 // should be incremental with periodic yields.
3563 _markBitMap.iterate(&markFromRootsClosure);
3564 // If _restart_addr is non-NULL, a marking stack overflow
3565 // occurred; we need to do a fresh iteration from the
3566 // indicated restart address.
3567 while (_restart_addr != NULL) {
3568 if (_foregroundGCIsActive) {
3569 // We may be running into repeated stack overflows, having
3570 // reached the limit of the stack size, while making very
3571 // slow forward progress. It may be best to bail out and
3572 // let the foreground collector do its job.
3573 // Clear _restart_addr, so that foreground GC
3574 // works from scratch. This avoids the headache of
3575 // a "rescan" which would otherwise be needed because
3576 // of the dirty mod union table & card table.
3577 _restart_addr = NULL;
3578 return false; // indicating failure to complete marking
3579 }
3580 // Deal with stack overflow:
3581 // we restart marking from _restart_addr
3582 HeapWord* ra = _restart_addr;
3583 markFromRootsClosure.reset(ra);
3584 _restart_addr = NULL;
3585 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
3586 }
3587 return true;
3588 }
3589
3590 void CMSCollector::preclean() {
3591 check_correct_thread_executing();
3592 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
3593 verify_work_stacks_empty();
3594 verify_overflow_empty();
3595 _abort_preclean = false;
3596 if (CMSPrecleaningEnabled) {
3597 if (!CMSEdenChunksRecordAlways) {
3598 _eden_chunk_index = 0;
3599 }
3600 size_t used = get_eden_used();
3601 size_t capacity = get_eden_capacity();
3602 // Don't start sampling unless we will get sufficiently
3603 // many samples.
3604 if (used < (((capacity / CMSScheduleRemarkSamplingRatio) / 100)
3605 * CMSScheduleRemarkEdenPenetration)) {
3606 _start_sampling = true;
3607 } else {
3608 _start_sampling = false;
3609 }
3610 GCTraceCPUTime tcpu;
3611 CMSPhaseAccounting pa(this, "Concurrent Preclean");
3612 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
3613 }
3614 CMSTokenSync x(true); // is cms thread
3615 if (CMSPrecleaningEnabled) {
3616 sample_eden();
3617 _collectorState = AbortablePreclean;
3618 } else {
3619 _collectorState = FinalMarking;
3620 }
3621 verify_work_stacks_empty();
3622 verify_overflow_empty();
3623 }
3624
3625 // Try and schedule the remark such that young gen
3626 // occupancy is CMSScheduleRemarkEdenPenetration %.
3627 void CMSCollector::abortable_preclean() {
3628 check_correct_thread_executing();
3629 assert(CMSPrecleaningEnabled, "Inconsistent control state");
3630 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
3631
3632 // If Eden's current occupancy is below this threshold,
3633 // immediately schedule the remark; else preclean
3634 // past the next scavenge in an effort to
3635 // schedule the pause as described above. By choosing
3636 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
3637 // we will never do an actual abortable preclean cycle.
3638 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
3639 GCTraceCPUTime tcpu;
3640 CMSPhaseAccounting pa(this, "Concurrent Abortable Preclean");
3641 // We need more smarts in the abortable preclean
3642 // loop below to deal with cases where allocation
3643 // in young gen is very very slow, and our precleaning
3644 // is running a losing race against a horde of
3645 // mutators intent on flooding us with CMS updates
3646 // (dirty cards).
3647 // One, admittedly dumb, strategy is to give up
3648 // after a certain number of abortable precleaning loops
3649 // or after a certain maximum time. We want to make
3650 // this smarter in the next iteration.
3651 // XXX FIX ME!!! YSR
3652 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
3653 while (!(should_abort_preclean() ||
3654 ConcurrentMarkSweepThread::cmst()->should_terminate())) {
3655 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
3656 cumworkdone += workdone;
3657 loops++;
3658 // Voluntarily terminate abortable preclean phase if we have
3659 // been at it for too long.
3660 if ((CMSMaxAbortablePrecleanLoops != 0) &&
3661 loops >= CMSMaxAbortablePrecleanLoops) {
3662 log_debug(gc)(" CMS: abort preclean due to loops ");
3663 break;
3664 }
3665 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
3666 log_debug(gc)(" CMS: abort preclean due to time ");
3667 break;
3668 }
3669 // If we are doing little work each iteration, we should
3670 // take a short break.
3671 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
3672 // Sleep for some time, waiting for work to accumulate
3673 stopTimer();
3674 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
3675 startTimer();
3676 waited++;
3677 }
3678 }
3679 log_trace(gc)(" [" SIZE_FORMAT " iterations, " SIZE_FORMAT " waits, " SIZE_FORMAT " cards)] ",
3680 loops, waited, cumworkdone);
3681 }
3682 CMSTokenSync x(true); // is cms thread
3683 if (_collectorState != Idling) {
3684 assert(_collectorState == AbortablePreclean,
3685 "Spontaneous state transition?");
3686 _collectorState = FinalMarking;
3687 } // Else, a foreground collection completed this CMS cycle.
3688 return;
3689 }
3690
3691 // Respond to an Eden sampling opportunity
3692 void CMSCollector::sample_eden() {
3693 // Make sure a young gc cannot sneak in between our
3694 // reading and recording of a sample.
3695 assert(Thread::current()->is_ConcurrentGC_thread(),
3696 "Only the cms thread may collect Eden samples");
3697 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
3698 "Should collect samples while holding CMS token");
3699 if (!_start_sampling) {
3700 return;
3701 }
3702 // When CMSEdenChunksRecordAlways is true, the eden chunk array
3703 // is populated by the young generation.
3704 if (_eden_chunk_array != NULL && !CMSEdenChunksRecordAlways) {
3705 if (_eden_chunk_index < _eden_chunk_capacity) {
3706 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
3707 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
3708 "Unexpected state of Eden");
3709 // We'd like to check that what we just sampled is an oop-start address;
3710 // however, we cannot do that here since the object may not yet have been
3711 // initialized. So we'll instead do the check when we _use_ this sample
3712 // later.
3713 if (_eden_chunk_index == 0 ||
3714 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
3715 _eden_chunk_array[_eden_chunk_index-1])
3716 >= CMSSamplingGrain)) {
3717 _eden_chunk_index++; // commit sample
3718 }
3719 }
3720 }
3721 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
3722 size_t used = get_eden_used();
3723 size_t capacity = get_eden_capacity();
3724 assert(used <= capacity, "Unexpected state of Eden");
3725 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
3726 _abort_preclean = true;
3727 }
3728 }
3729 }
3730
3731
3732 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
3733 assert(_collectorState == Precleaning ||
3734 _collectorState == AbortablePreclean, "incorrect state");
3735 ResourceMark rm;
3736 HandleMark hm;
3737
3738 // Precleaning is currently not MT but the reference processor
3739 // may be set for MT. Disable it temporarily here.
3740 ReferenceProcessor* rp = ref_processor();
3741 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
3742
3743 // Do one pass of scrubbing the discovered reference lists
3744 // to remove any reference objects with strongly-reachable
3745 // referents.
3746 if (clean_refs) {
3747 CMSPrecleanRefsYieldClosure yield_cl(this);
3748 assert(rp->span().equals(_span), "Spans should be equal");
3749 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
3750 &_markStack, true /* preclean */);
3751 CMSDrainMarkingStackClosure complete_trace(this,
3752 _span, &_markBitMap, &_markStack,
3753 &keep_alive, true /* preclean */);
3754
3755 // We don't want this step to interfere with a young
3756 // collection because we don't want to take CPU
3757 // or memory bandwidth away from the young GC threads
3758 // (which may be as many as there are CPUs).
3759 // Note that we don't need to protect ourselves from
3760 // interference with mutators because they can't
3761 // manipulate the discovered reference lists nor affect
3762 // the computed reachability of the referents, the
3763 // only properties manipulated by the precleaning
3764 // of these reference lists.
3765 stopTimer();
3766 CMSTokenSyncWithLocks x(true /* is cms thread */,
3767 bitMapLock());
3768 startTimer();
3769 sample_eden();
3770
3771 // The following will yield to allow foreground
3772 // collection to proceed promptly. XXX YSR:
3773 // The code in this method may need further
3774 // tweaking for better performance and some restructuring
3775 // for cleaner interfaces.
3776 GCTimer *gc_timer = NULL; // Currently not tracing concurrent phases
3777 rp->preclean_discovered_references(
3778 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl,
3779 gc_timer);
3780 }
3781
3782 if (clean_survivor) { // preclean the active survivor space(s)
3783 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
3784 &_markBitMap, &_modUnionTable,
3785 &_markStack, true /* precleaning phase */);
3786 stopTimer();
3787 CMSTokenSyncWithLocks ts(true /* is cms thread */,
3788 bitMapLock());
3789 startTimer();
3790 unsigned int before_count =
3791 GenCollectedHeap::heap()->total_collections();
3792 SurvivorSpacePrecleanClosure
3793 sss_cl(this, _span, &_markBitMap, &_markStack,
3794 &pam_cl, before_count, CMSYield);
3795 _young_gen->from()->object_iterate_careful(&sss_cl);
3796 _young_gen->to()->object_iterate_careful(&sss_cl);
3797 }
3798 MarkRefsIntoAndScanClosure
3799 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
3800 &_markStack, this, CMSYield,
3801 true /* precleaning phase */);
3802 // CAUTION: The following closure has persistent state that may need to
3803 // be reset upon a decrease in the sequence of addresses it
3804 // processes.
3805 ScanMarkedObjectsAgainCarefullyClosure
3806 smoac_cl(this, _span,
3807 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
3808
3809 // Preclean dirty cards in ModUnionTable and CardTable using
3810 // appropriate convergence criterion;
3811 // repeat CMSPrecleanIter times unless we find that
3812 // we are losing.
3813 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
3814 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
3815 "Bad convergence multiplier");
3816 assert(CMSPrecleanThreshold >= 100,
3817 "Unreasonably low CMSPrecleanThreshold");
3818
3819 size_t numIter, cumNumCards, lastNumCards, curNumCards;
3820 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
3821 numIter < CMSPrecleanIter;
3822 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
3823 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
3824 log_trace(gc)(" (modUnionTable: " SIZE_FORMAT " cards)", curNumCards);
3825 // Either there are very few dirty cards, so re-mark
3826 // pause will be small anyway, or our pre-cleaning isn't
3827 // that much faster than the rate at which cards are being
3828 // dirtied, so we might as well stop and re-mark since
3829 // precleaning won't improve our re-mark time by much.
3830 if (curNumCards <= CMSPrecleanThreshold ||
3831 (numIter > 0 &&
3832 (curNumCards * CMSPrecleanDenominator >
3833 lastNumCards * CMSPrecleanNumerator))) {
3834 numIter++;
3835 cumNumCards += curNumCards;
3836 break;
3837 }
3838 }
3839
3840 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
3841
3842 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
3843 cumNumCards += curNumCards;
3844 log_trace(gc)(" (cardTable: " SIZE_FORMAT " cards, re-scanned " SIZE_FORMAT " cards, " SIZE_FORMAT " iterations)",
3845 curNumCards, cumNumCards, numIter);
3846 return cumNumCards; // as a measure of useful work done
3847 }
3848
3849 // PRECLEANING NOTES:
3850 // Precleaning involves:
3851 // . reading the bits of the modUnionTable and clearing the set bits.
3852 // . For the cards corresponding to the set bits, we scan the
3853 // objects on those cards. This means we need the free_list_lock
3854 // so that we can safely iterate over the CMS space when scanning
3855 // for oops.
3856 // . When we scan the objects, we'll be both reading and setting
3857 // marks in the marking bit map, so we'll need the marking bit map.
3858 // . For protecting _collector_state transitions, we take the CGC_lock.
3859 // Note that any races in the reading of of card table entries by the
3860 // CMS thread on the one hand and the clearing of those entries by the
3861 // VM thread or the setting of those entries by the mutator threads on the
3862 // other are quite benign. However, for efficiency it makes sense to keep
3863 // the VM thread from racing with the CMS thread while the latter is
3864 // dirty card info to the modUnionTable. We therefore also use the
3865 // CGC_lock to protect the reading of the card table and the mod union
3866 // table by the CM thread.
3867 // . We run concurrently with mutator updates, so scanning
3868 // needs to be done carefully -- we should not try to scan
3869 // potentially uninitialized objects.
3870 //
3871 // Locking strategy: While holding the CGC_lock, we scan over and
3872 // reset a maximal dirty range of the mod union / card tables, then lock
3873 // the free_list_lock and bitmap lock to do a full marking, then
3874 // release these locks; and repeat the cycle. This allows for a
3875 // certain amount of fairness in the sharing of these locks between
3876 // the CMS collector on the one hand, and the VM thread and the
3877 // mutators on the other.
3878
3879 // NOTE: preclean_mod_union_table() and preclean_card_table()
3880 // further below are largely identical; if you need to modify
3881 // one of these methods, please check the other method too.
3882
3883 size_t CMSCollector::preclean_mod_union_table(
3884 ConcurrentMarkSweepGeneration* old_gen,
3885 ScanMarkedObjectsAgainCarefullyClosure* cl) {
3886 verify_work_stacks_empty();
3887 verify_overflow_empty();
3888
3889 // strategy: starting with the first card, accumulate contiguous
3890 // ranges of dirty cards; clear these cards, then scan the region
3891 // covered by these cards.
3892
3893 // Since all of the MUT is committed ahead, we can just use
3894 // that, in case the generations expand while we are precleaning.
3895 // It might also be fine to just use the committed part of the
3896 // generation, but we might potentially miss cards when the
3897 // generation is rapidly expanding while we are in the midst
3898 // of precleaning.
3899 HeapWord* startAddr = old_gen->reserved().start();
3900 HeapWord* endAddr = old_gen->reserved().end();
3901
3902 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
3903
3904 size_t numDirtyCards, cumNumDirtyCards;
3905 HeapWord *nextAddr, *lastAddr;
3906 for (cumNumDirtyCards = numDirtyCards = 0,
3907 nextAddr = lastAddr = startAddr;
3908 nextAddr < endAddr;
3909 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
3910
3911 ResourceMark rm;
3912 HandleMark hm;
3913
3914 MemRegion dirtyRegion;
3915 {
3916 stopTimer();
3917 // Potential yield point
3918 CMSTokenSync ts(true);
3919 startTimer();
3920 sample_eden();
3921 // Get dirty region starting at nextOffset (inclusive),
3922 // simultaneously clearing it.
3923 dirtyRegion =
3924 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
3925 assert(dirtyRegion.start() >= nextAddr,
3926 "returned region inconsistent?");
3927 }
3928 // Remember where the next search should begin.
3929 // The returned region (if non-empty) is a right open interval,
3930 // so lastOffset is obtained from the right end of that
3931 // interval.
3932 lastAddr = dirtyRegion.end();
3933 // Should do something more transparent and less hacky XXX
3934 numDirtyCards =
3935 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
3936
3937 // We'll scan the cards in the dirty region (with periodic
3938 // yields for foreground GC as needed).
3939 if (!dirtyRegion.is_empty()) {
3940 assert(numDirtyCards > 0, "consistency check");
3941 HeapWord* stop_point = NULL;
3942 stopTimer();
3943 // Potential yield point
3944 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(),
3945 bitMapLock());
3946 startTimer();
3947 {
3948 verify_work_stacks_empty();
3949 verify_overflow_empty();
3950 sample_eden();
3951 stop_point =
3952 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
3953 }
3954 if (stop_point != NULL) {
3955 // The careful iteration stopped early either because it found an
3956 // uninitialized object, or because we were in the midst of an
3957 // "abortable preclean", which should now be aborted. Redirty
3958 // the bits corresponding to the partially-scanned or unscanned
3959 // cards. We'll either restart at the next block boundary or
3960 // abort the preclean.
3961 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
3962 "Should only be AbortablePreclean.");
3963 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
3964 if (should_abort_preclean()) {
3965 break; // out of preclean loop
3966 } else {
3967 // Compute the next address at which preclean should pick up;
3968 // might need bitMapLock in order to read P-bits.
3969 lastAddr = next_card_start_after_block(stop_point);
3970 }
3971 }
3972 } else {
3973 assert(lastAddr == endAddr, "consistency check");
3974 assert(numDirtyCards == 0, "consistency check");
3975 break;
3976 }
3977 }
3978 verify_work_stacks_empty();
3979 verify_overflow_empty();
3980 return cumNumDirtyCards;
3981 }
3982
3983 // NOTE: preclean_mod_union_table() above and preclean_card_table()
3984 // below are largely identical; if you need to modify
3985 // one of these methods, please check the other method too.
3986
3987 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* old_gen,
3988 ScanMarkedObjectsAgainCarefullyClosure* cl) {
3989 // strategy: it's similar to precleamModUnionTable above, in that
3990 // we accumulate contiguous ranges of dirty cards, mark these cards
3991 // precleaned, then scan the region covered by these cards.
3992 HeapWord* endAddr = (HeapWord*)(old_gen->_virtual_space.high());
3993 HeapWord* startAddr = (HeapWord*)(old_gen->_virtual_space.low());
3994
3995 cl->setFreelistLock(old_gen->freelistLock()); // needed for yielding
3996
3997 size_t numDirtyCards, cumNumDirtyCards;
3998 HeapWord *lastAddr, *nextAddr;
3999
4000 for (cumNumDirtyCards = numDirtyCards = 0,
4001 nextAddr = lastAddr = startAddr;
4002 nextAddr < endAddr;
4003 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4004
4005 ResourceMark rm;
4006 HandleMark hm;
4007
4008 MemRegion dirtyRegion;
4009 {
4010 // See comments in "Precleaning notes" above on why we
4011 // do this locking. XXX Could the locking overheads be
4012 // too high when dirty cards are sparse? [I don't think so.]
4013 stopTimer();
4014 CMSTokenSync x(true); // is cms thread
4015 startTimer();
4016 sample_eden();
4017 // Get and clear dirty region from card table
4018 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4019 MemRegion(nextAddr, endAddr),
4020 true,
4021 CardTableModRefBS::precleaned_card_val());
4022
4023 assert(dirtyRegion.start() >= nextAddr,
4024 "returned region inconsistent?");
4025 }
4026 lastAddr = dirtyRegion.end();
4027 numDirtyCards =
4028 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4029
4030 if (!dirtyRegion.is_empty()) {
4031 stopTimer();
4032 CMSTokenSyncWithLocks ts(true, old_gen->freelistLock(), bitMapLock());
4033 startTimer();
4034 sample_eden();
4035 verify_work_stacks_empty();
4036 verify_overflow_empty();
4037 HeapWord* stop_point =
4038 old_gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4039 if (stop_point != NULL) {
4040 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4041 "Should only be AbortablePreclean.");
4042 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4043 if (should_abort_preclean()) {
4044 break; // out of preclean loop
4045 } else {
4046 // Compute the next address at which preclean should pick up.
4047 lastAddr = next_card_start_after_block(stop_point);
4048 }
4049 }
4050 } else {
4051 break;
4052 }
4053 }
4054 verify_work_stacks_empty();
4055 verify_overflow_empty();
4056 return cumNumDirtyCards;
4057 }
4058
4059 class PrecleanKlassClosure : public KlassClosure {
4060 KlassToOopClosure _cm_klass_closure;
4061 public:
4062 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4063 void do_klass(Klass* k) {
4064 if (k->has_accumulated_modified_oops()) {
4065 k->clear_accumulated_modified_oops();
4066
4067 _cm_klass_closure.do_klass(k);
4068 }
4069 }
4070 };
4071
4072 // The freelist lock is needed to prevent asserts, is it really needed?
4073 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4074
4075 cl->set_freelistLock(freelistLock);
4076
4077 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4078
4079 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4080 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4081 PrecleanKlassClosure preclean_klass_closure(cl);
4082 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4083
4084 verify_work_stacks_empty();
4085 verify_overflow_empty();
4086 }
4087
4088 void CMSCollector::checkpointRootsFinal() {
4089 assert(_collectorState == FinalMarking, "incorrect state transition?");
4090 check_correct_thread_executing();
4091 // world is stopped at this checkpoint
4092 assert(SafepointSynchronize::is_at_safepoint(),
4093 "world should be stopped");
4094 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4095
4096 verify_work_stacks_empty();
4097 verify_overflow_empty();
4098
4099 log_debug(gc)("YG occupancy: " SIZE_FORMAT " K (" SIZE_FORMAT " K)",
4100 _young_gen->used() / K, _young_gen->capacity() / K);
4101 {
4102 if (CMSScavengeBeforeRemark) {
4103 GenCollectedHeap* gch = GenCollectedHeap::heap();
4104 // Temporarily set flag to false, GCH->do_collection will
4105 // expect it to be false and set to true
4106 FlagSetting fl(gch->_is_gc_active, false);
4107
4108 gch->do_collection(true, // full (i.e. force, see below)
4109 false, // !clear_all_soft_refs
4110 0, // size
4111 false, // is_tlab
4112 GenCollectedHeap::YoungGen // type
4113 );
4114 }
4115 FreelistLocker x(this);
4116 MutexLockerEx y(bitMapLock(),
4117 Mutex::_no_safepoint_check_flag);
4118 checkpointRootsFinalWork();
4119 }
4120 verify_work_stacks_empty();
4121 verify_overflow_empty();
4122 }
4123
4124 void CMSCollector::checkpointRootsFinalWork() {
4125 GCTraceTime(Trace, gc, phases) tm("checkpointRootsFinalWork", _gc_timer_cm);
4126
4127 assert(haveFreelistLocks(), "must have free list locks");
4128 assert_lock_strong(bitMapLock());
4129
4130 ResourceMark rm;
4131 HandleMark hm;
4132
4133 GenCollectedHeap* gch = GenCollectedHeap::heap();
4134
4135 if (should_unload_classes()) {
4136 CodeCache::gc_prologue();
4137 }
4138 assert(haveFreelistLocks(), "must have free list locks");
4139 assert_lock_strong(bitMapLock());
4140
4141 // We might assume that we need not fill TLAB's when
4142 // CMSScavengeBeforeRemark is set, because we may have just done
4143 // a scavenge which would have filled all TLAB's -- and besides
4144 // Eden would be empty. This however may not always be the case --
4145 // for instance although we asked for a scavenge, it may not have
4146 // happened because of a JNI critical section. We probably need
4147 // a policy for deciding whether we can in that case wait until
4148 // the critical section releases and then do the remark following
4149 // the scavenge, and skip it here. In the absence of that policy,
4150 // or of an indication of whether the scavenge did indeed occur,
4151 // we cannot rely on TLAB's having been filled and must do
4152 // so here just in case a scavenge did not happen.
4153 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4154 // Update the saved marks which may affect the root scans.
4155 gch->save_marks();
4156
4157 print_eden_and_survivor_chunk_arrays();
4158
4159 {
4160 #if defined(COMPILER2) || INCLUDE_JVMCI
4161 DerivedPointerTableDeactivate dpt_deact;
4162 #endif
4163
4164 // Note on the role of the mod union table:
4165 // Since the marker in "markFromRoots" marks concurrently with
4166 // mutators, it is possible for some reachable objects not to have been
4167 // scanned. For instance, an only reference to an object A was
4168 // placed in object B after the marker scanned B. Unless B is rescanned,
4169 // A would be collected. Such updates to references in marked objects
4170 // are detected via the mod union table which is the set of all cards
4171 // dirtied since the first checkpoint in this GC cycle and prior to
4172 // the most recent young generation GC, minus those cleaned up by the
4173 // concurrent precleaning.
4174 if (CMSParallelRemarkEnabled) {
4175 GCTraceTime(Debug, gc, phases) t("Rescan (parallel)", _gc_timer_cm);
4176 do_remark_parallel();
4177 } else {
4178 GCTraceTime(Debug, gc, phases) t("Rescan (non-parallel)", _gc_timer_cm);
4179 do_remark_non_parallel();
4180 }
4181 }
4182 verify_work_stacks_empty();
4183 verify_overflow_empty();
4184
4185 {
4186 GCTraceTime(Trace, gc, phases) ts("refProcessingWork", _gc_timer_cm);
4187 refProcessingWork();
4188 }
4189 verify_work_stacks_empty();
4190 verify_overflow_empty();
4191
4192 if (should_unload_classes()) {
4193 CodeCache::gc_epilogue();
4194 }
4195 JvmtiExport::gc_epilogue();
4196
4197 // If we encountered any (marking stack / work queue) overflow
4198 // events during the current CMS cycle, take appropriate
4199 // remedial measures, where possible, so as to try and avoid
4200 // recurrence of that condition.
4201 assert(_markStack.isEmpty(), "No grey objects");
4202 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4203 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4204 if (ser_ovflw > 0) {
4205 log_trace(gc)("Marking stack overflow (benign) (pmc_pc=" SIZE_FORMAT ", pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ", kac_preclean=" SIZE_FORMAT ")",
4206 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4207 _markStack.expand();
4208 _ser_pmc_remark_ovflw = 0;
4209 _ser_pmc_preclean_ovflw = 0;
4210 _ser_kac_preclean_ovflw = 0;
4211 _ser_kac_ovflw = 0;
4212 }
4213 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4214 log_trace(gc)("Work queue overflow (benign) (pmc_rm=" SIZE_FORMAT ", kac=" SIZE_FORMAT ")",
4215 _par_pmc_remark_ovflw, _par_kac_ovflw);
4216 _par_pmc_remark_ovflw = 0;
4217 _par_kac_ovflw = 0;
4218 }
4219 if (_markStack._hit_limit > 0) {
4220 log_trace(gc)(" (benign) Hit max stack size limit (" SIZE_FORMAT ")",
4221 _markStack._hit_limit);
4222 }
4223 if (_markStack._failed_double > 0) {
4224 log_trace(gc)(" (benign) Failed stack doubling (" SIZE_FORMAT "), current capacity " SIZE_FORMAT,
4225 _markStack._failed_double, _markStack.capacity());
4226 }
4227 _markStack._hit_limit = 0;
4228 _markStack._failed_double = 0;
4229
4230 if ((VerifyAfterGC || VerifyDuringGC) &&
4231 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4232 verify_after_remark();
4233 }
4234
4235 _gc_tracer_cm->report_object_count_after_gc(&_is_alive_closure);
4236
4237 // Change under the freelistLocks.
4238 _collectorState = Sweeping;
4239 // Call isAllClear() under bitMapLock
4240 assert(_modUnionTable.isAllClear(),
4241 "Should be clear by end of the final marking");
4242 assert(_ct->klass_rem_set()->mod_union_is_clear(),
4243 "Should be clear by end of the final marking");
4244 }
4245
4246 void CMSParInitialMarkTask::work(uint worker_id) {
4247 elapsedTimer _timer;
4248 ResourceMark rm;
4249 HandleMark hm;
4250
4251 // ---------- scan from roots --------------
4252 _timer.start();
4253 GenCollectedHeap* gch = GenCollectedHeap::heap();
4254 ParMarkRefsIntoClosure par_mri_cl(_collector->_span, &(_collector->_markBitMap));
4255
4256 // ---------- young gen roots --------------
4257 {
4258 work_on_young_gen_roots(&par_mri_cl);
4259 _timer.stop();
4260 log_trace(gc, task)("Finished young gen initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4261 }
4262
4263 // ---------- remaining roots --------------
4264 _timer.reset();
4265 _timer.start();
4266
4267 CLDToOopClosure cld_closure(&par_mri_cl, true);
4268
4269 gch->gen_process_roots(_strong_roots_scope,
4270 GenCollectedHeap::OldGen,
4271 false, // yg was scanned above
4272 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4273 _collector->should_unload_classes(),
4274 &par_mri_cl,
4275 NULL,
4276 &cld_closure);
4277 assert(_collector->should_unload_classes()
4278 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4279 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4280 _timer.stop();
4281 log_trace(gc, task)("Finished remaining root initial mark scan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4282 }
4283
4284 // Parallel remark task
4285 class CMSParRemarkTask: public CMSParMarkTask {
4286 CompactibleFreeListSpace* _cms_space;
4287
4288 // The per-thread work queues, available here for stealing.
4289 OopTaskQueueSet* _task_queues;
4290 ParallelTaskTerminator _term;
4291 StrongRootsScope* _strong_roots_scope;
4292
4293 public:
4294 // A value of 0 passed to n_workers will cause the number of
4295 // workers to be taken from the active workers in the work gang.
4296 CMSParRemarkTask(CMSCollector* collector,
4297 CompactibleFreeListSpace* cms_space,
4298 uint n_workers, WorkGang* workers,
4299 OopTaskQueueSet* task_queues,
4300 StrongRootsScope* strong_roots_scope):
4301 CMSParMarkTask("Rescan roots and grey objects in parallel",
4302 collector, n_workers),
4303 _cms_space(cms_space),
4304 _task_queues(task_queues),
4305 _term(n_workers, task_queues),
4306 _strong_roots_scope(strong_roots_scope) { }
4307
4308 OopTaskQueueSet* task_queues() { return _task_queues; }
4309
4310 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
4311
4312 ParallelTaskTerminator* terminator() { return &_term; }
4313 uint n_workers() { return _n_workers; }
4314
4315 void work(uint worker_id);
4316
4317 private:
4318 // ... of dirty cards in old space
4319 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
4320 ParMarkRefsIntoAndScanClosure* cl);
4321
4322 // ... work stealing for the above
4323 void do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl, int* seed);
4324 };
4325
4326 class RemarkKlassClosure : public KlassClosure {
4327 KlassToOopClosure _cm_klass_closure;
4328 public:
4329 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4330 void do_klass(Klass* k) {
4331 // Check if we have modified any oops in the Klass during the concurrent marking.
4332 if (k->has_accumulated_modified_oops()) {
4333 k->clear_accumulated_modified_oops();
4334
4335 // We could have transfered the current modified marks to the accumulated marks,
4336 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
4337 } else if (k->has_modified_oops()) {
4338 // Don't clear anything, this info is needed by the next young collection.
4339 } else {
4340 // No modified oops in the Klass.
4341 return;
4342 }
4343
4344 // The klass has modified fields, need to scan the klass.
4345 _cm_klass_closure.do_klass(k);
4346 }
4347 };
4348
4349 void CMSParMarkTask::work_on_young_gen_roots(OopsInGenClosure* cl) {
4350 ParNewGeneration* young_gen = _collector->_young_gen;
4351 ContiguousSpace* eden_space = young_gen->eden();
4352 ContiguousSpace* from_space = young_gen->from();
4353 ContiguousSpace* to_space = young_gen->to();
4354
4355 HeapWord** eca = _collector->_eden_chunk_array;
4356 size_t ect = _collector->_eden_chunk_index;
4357 HeapWord** sca = _collector->_survivor_chunk_array;
4358 size_t sct = _collector->_survivor_chunk_index;
4359
4360 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
4361 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
4362
4363 do_young_space_rescan(cl, to_space, NULL, 0);
4364 do_young_space_rescan(cl, from_space, sca, sct);
4365 do_young_space_rescan(cl, eden_space, eca, ect);
4366 }
4367
4368 // work_queue(i) is passed to the closure
4369 // ParMarkRefsIntoAndScanClosure. The "i" parameter
4370 // also is passed to do_dirty_card_rescan_tasks() and to
4371 // do_work_steal() to select the i-th task_queue.
4372
4373 void CMSParRemarkTask::work(uint worker_id) {
4374 elapsedTimer _timer;
4375 ResourceMark rm;
4376 HandleMark hm;
4377
4378 // ---------- rescan from roots --------------
4379 _timer.start();
4380 GenCollectedHeap* gch = GenCollectedHeap::heap();
4381 ParMarkRefsIntoAndScanClosure par_mrias_cl(_collector,
4382 _collector->_span, _collector->ref_processor(),
4383 &(_collector->_markBitMap),
4384 work_queue(worker_id));
4385
4386 // Rescan young gen roots first since these are likely
4387 // coarsely partitioned and may, on that account, constitute
4388 // the critical path; thus, it's best to start off that
4389 // work first.
4390 // ---------- young gen roots --------------
4391 {
4392 work_on_young_gen_roots(&par_mrias_cl);
4393 _timer.stop();
4394 log_trace(gc, task)("Finished young gen rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4395 }
4396
4397 // ---------- remaining roots --------------
4398 _timer.reset();
4399 _timer.start();
4400 gch->gen_process_roots(_strong_roots_scope,
4401 GenCollectedHeap::OldGen,
4402 false, // yg was scanned above
4403 GenCollectedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
4404 _collector->should_unload_classes(),
4405 &par_mrias_cl,
4406 NULL,
4407 NULL); // The dirty klasses will be handled below
4408
4409 assert(_collector->should_unload_classes()
4410 || (_collector->CMSCollector::roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4411 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4412 _timer.stop();
4413 log_trace(gc, task)("Finished remaining root rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4414
4415 // ---------- unhandled CLD scanning ----------
4416 if (worker_id == 0) { // Single threaded at the moment.
4417 _timer.reset();
4418 _timer.start();
4419
4420 // Scan all new class loader data objects and new dependencies that were
4421 // introduced during concurrent marking.
4422 ResourceMark rm;
4423 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4424 for (int i = 0; i < array->length(); i++) {
4425 par_mrias_cl.do_cld_nv(array->at(i));
4426 }
4427
4428 // We don't need to keep track of new CLDs anymore.
4429 ClassLoaderDataGraph::remember_new_clds(false);
4430
4431 _timer.stop();
4432 log_trace(gc, task)("Finished unhandled CLD scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4433 }
4434
4435 // ---------- dirty klass scanning ----------
4436 if (worker_id == 0) { // Single threaded at the moment.
4437 _timer.reset();
4438 _timer.start();
4439
4440 // Scan all classes that was dirtied during the concurrent marking phase.
4441 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
4442 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4443
4444 _timer.stop();
4445 log_trace(gc, task)("Finished dirty klass scanning work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4446 }
4447
4448 // We might have added oops to ClassLoaderData::_handles during the
4449 // concurrent marking phase. These oops point to newly allocated objects
4450 // that are guaranteed to be kept alive. Either by the direct allocation
4451 // code, or when the young collector processes the roots. Hence,
4452 // we don't have to revisit the _handles block during the remark phase.
4453
4454 // ---------- rescan dirty cards ------------
4455 _timer.reset();
4456 _timer.start();
4457
4458 // Do the rescan tasks for each of the two spaces
4459 // (cms_space) in turn.
4460 // "worker_id" is passed to select the task_queue for "worker_id"
4461 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
4462 _timer.stop();
4463 log_trace(gc, task)("Finished dirty card rescan work in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4464
4465 // ---------- steal work from other threads ...
4466 // ---------- ... and drain overflow list.
4467 _timer.reset();
4468 _timer.start();
4469 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
4470 _timer.stop();
4471 log_trace(gc, task)("Finished work stealing in %dth thread: %3.3f sec", worker_id, _timer.seconds());
4472 }
4473
4474 void
4475 CMSParMarkTask::do_young_space_rescan(
4476 OopsInGenClosure* cl, ContiguousSpace* space,
4477 HeapWord** chunk_array, size_t chunk_top) {
4478 // Until all tasks completed:
4479 // . claim an unclaimed task
4480 // . compute region boundaries corresponding to task claimed
4481 // using chunk_array
4482 // . par_oop_iterate(cl) over that region
4483
4484 ResourceMark rm;
4485 HandleMark hm;
4486
4487 SequentialSubTasksDone* pst = space->par_seq_tasks();
4488
4489 uint nth_task = 0;
4490 uint n_tasks = pst->n_tasks();
4491
4492 if (n_tasks > 0) {
4493 assert(pst->valid(), "Uninitialized use?");
4494 HeapWord *start, *end;
4495 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4496 // We claimed task # nth_task; compute its boundaries.
4497 if (chunk_top == 0) { // no samples were taken
4498 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 eden task");
4499 start = space->bottom();
4500 end = space->top();
4501 } else if (nth_task == 0) {
4502 start = space->bottom();
4503 end = chunk_array[nth_task];
4504 } else if (nth_task < (uint)chunk_top) {
4505 assert(nth_task >= 1, "Control point invariant");
4506 start = chunk_array[nth_task - 1];
4507 end = chunk_array[nth_task];
4508 } else {
4509 assert(nth_task == (uint)chunk_top, "Control point invariant");
4510 start = chunk_array[chunk_top - 1];
4511 end = space->top();
4512 }
4513 MemRegion mr(start, end);
4514 // Verify that mr is in space
4515 assert(mr.is_empty() || space->used_region().contains(mr),
4516 "Should be in space");
4517 // Verify that "start" is an object boundary
4518 assert(mr.is_empty() || oop(mr.start())->is_oop(),
4519 "Should be an oop");
4520 space->par_oop_iterate(mr, cl);
4521 }
4522 pst->all_tasks_completed();
4523 }
4524 }
4525
4526 void
4527 CMSParRemarkTask::do_dirty_card_rescan_tasks(
4528 CompactibleFreeListSpace* sp, int i,
4529 ParMarkRefsIntoAndScanClosure* cl) {
4530 // Until all tasks completed:
4531 // . claim an unclaimed task
4532 // . compute region boundaries corresponding to task claimed
4533 // . transfer dirty bits ct->mut for that region
4534 // . apply rescanclosure to dirty mut bits for that region
4535
4536 ResourceMark rm;
4537 HandleMark hm;
4538
4539 OopTaskQueue* work_q = work_queue(i);
4540 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
4541 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
4542 // CAUTION: This closure has state that persists across calls to
4543 // the work method dirty_range_iterate_clear() in that it has
4544 // embedded in it a (subtype of) UpwardsObjectClosure. The
4545 // use of that state in the embedded UpwardsObjectClosure instance
4546 // assumes that the cards are always iterated (even if in parallel
4547 // by several threads) in monotonically increasing order per each
4548 // thread. This is true of the implementation below which picks
4549 // card ranges (chunks) in monotonically increasing order globally
4550 // and, a-fortiori, in monotonically increasing order per thread
4551 // (the latter order being a subsequence of the former).
4552 // If the work code below is ever reorganized into a more chaotic
4553 // work-partitioning form than the current "sequential tasks"
4554 // paradigm, the use of that persistent state will have to be
4555 // revisited and modified appropriately. See also related
4556 // bug 4756801 work on which should examine this code to make
4557 // sure that the changes there do not run counter to the
4558 // assumptions made here and necessary for correctness and
4559 // efficiency. Note also that this code might yield inefficient
4560 // behavior in the case of very large objects that span one or
4561 // more work chunks. Such objects would potentially be scanned
4562 // several times redundantly. Work on 4756801 should try and
4563 // address that performance anomaly if at all possible. XXX
4564 MemRegion full_span = _collector->_span;
4565 CMSBitMap* bm = &(_collector->_markBitMap); // shared
4566 MarkFromDirtyCardsClosure
4567 greyRescanClosure(_collector, full_span, // entire span of interest
4568 sp, bm, work_q, cl);
4569
4570 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
4571 assert(pst->valid(), "Uninitialized use?");
4572 uint nth_task = 0;
4573 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
4574 MemRegion span = sp->used_region();
4575 HeapWord* start_addr = span.start();
4576 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
4577 alignment);
4578 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
4579 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
4580 start_addr, "Check alignment");
4581 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
4582 chunk_size, "Check alignment");
4583
4584 while (!pst->is_task_claimed(/* reference */ nth_task)) {
4585 // Having claimed the nth_task, compute corresponding mem-region,
4586 // which is a-fortiori aligned correctly (i.e. at a MUT boundary).
4587 // The alignment restriction ensures that we do not need any
4588 // synchronization with other gang-workers while setting or
4589 // clearing bits in thus chunk of the MUT.
4590 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
4591 start_addr + (nth_task+1)*chunk_size);
4592 // The last chunk's end might be way beyond end of the
4593 // used region. In that case pull back appropriately.
4594 if (this_span.end() > end_addr) {
4595 this_span.set_end(end_addr);
4596 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
4597 }
4598 // Iterate over the dirty cards covering this chunk, marking them
4599 // precleaned, and setting the corresponding bits in the mod union
4600 // table. Since we have been careful to partition at Card and MUT-word
4601 // boundaries no synchronization is needed between parallel threads.
4602 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
4603 &modUnionClosure);
4604
4605 // Having transferred these marks into the modUnionTable,
4606 // rescan the marked objects on the dirty cards in the modUnionTable.
4607 // Even if this is at a synchronous collection, the initial marking
4608 // may have been done during an asynchronous collection so there
4609 // may be dirty bits in the mod-union table.
4610 _collector->_modUnionTable.dirty_range_iterate_clear(
4611 this_span, &greyRescanClosure);
4612 _collector->_modUnionTable.verifyNoOneBitsInRange(
4613 this_span.start(),
4614 this_span.end());
4615 }
4616 pst->all_tasks_completed(); // declare that i am done
4617 }
4618
4619 // . see if we can share work_queues with ParNew? XXX
4620 void
4621 CMSParRemarkTask::do_work_steal(int i, ParMarkRefsIntoAndScanClosure* cl,
4622 int* seed) {
4623 OopTaskQueue* work_q = work_queue(i);
4624 NOT_PRODUCT(int num_steals = 0;)
4625 oop obj_to_scan;
4626 CMSBitMap* bm = &(_collector->_markBitMap);
4627
4628 while (true) {
4629 // Completely finish any left over work from (an) earlier round(s)
4630 cl->trim_queue(0);
4631 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
4632 (size_t)ParGCDesiredObjsFromOverflowList);
4633 // Now check if there's any work in the overflow list
4634 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
4635 // only affects the number of attempts made to get work from the
4636 // overflow list and does not affect the number of workers. Just
4637 // pass ParallelGCThreads so this behavior is unchanged.
4638 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
4639 work_q,
4640 ParallelGCThreads)) {
4641 // found something in global overflow list;
4642 // not yet ready to go stealing work from others.
4643 // We'd like to assert(work_q->size() != 0, ...)
4644 // because we just took work from the overflow list,
4645 // but of course we can't since all of that could have
4646 // been already stolen from us.
4647 // "He giveth and He taketh away."
4648 continue;
4649 }
4650 // Verify that we have no work before we resort to stealing
4651 assert(work_q->size() == 0, "Have work, shouldn't steal");
4652 // Try to steal from other queues that have work
4653 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4654 NOT_PRODUCT(num_steals++;)
4655 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
4656 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
4657 // Do scanning work
4658 obj_to_scan->oop_iterate(cl);
4659 // Loop around, finish this work, and try to steal some more
4660 } else if (terminator()->offer_termination()) {
4661 break; // nirvana from the infinite cycle
4662 }
4663 }
4664 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
4665 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
4666 "Else our work is not yet done");
4667 }
4668
4669 // Record object boundaries in _eden_chunk_array by sampling the eden
4670 // top in the slow-path eden object allocation code path and record
4671 // the boundaries, if CMSEdenChunksRecordAlways is true. If
4672 // CMSEdenChunksRecordAlways is false, we use the other asynchronous
4673 // sampling in sample_eden() that activates during the part of the
4674 // preclean phase.
4675 void CMSCollector::sample_eden_chunk() {
4676 if (CMSEdenChunksRecordAlways && _eden_chunk_array != NULL) {
4677 if (_eden_chunk_lock->try_lock()) {
4678 // Record a sample. This is the critical section. The contents
4679 // of the _eden_chunk_array have to be non-decreasing in the
4680 // address order.
4681 _eden_chunk_array[_eden_chunk_index] = *_top_addr;
4682 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4683 "Unexpected state of Eden");
4684 if (_eden_chunk_index == 0 ||
4685 ((_eden_chunk_array[_eden_chunk_index] > _eden_chunk_array[_eden_chunk_index-1]) &&
4686 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4687 _eden_chunk_array[_eden_chunk_index-1]) >= CMSSamplingGrain))) {
4688 _eden_chunk_index++; // commit sample
4689 }
4690 _eden_chunk_lock->unlock();
4691 }
4692 }
4693 }
4694
4695 // Return a thread-local PLAB recording array, as appropriate.
4696 void* CMSCollector::get_data_recorder(int thr_num) {
4697 if (_survivor_plab_array != NULL &&
4698 (CMSPLABRecordAlways ||
4699 (_collectorState > Marking && _collectorState < FinalMarking))) {
4700 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
4701 ChunkArray* ca = &_survivor_plab_array[thr_num];
4702 ca->reset(); // clear it so that fresh data is recorded
4703 return (void*) ca;
4704 } else {
4705 return NULL;
4706 }
4707 }
4708
4709 // Reset all the thread-local PLAB recording arrays
4710 void CMSCollector::reset_survivor_plab_arrays() {
4711 for (uint i = 0; i < ParallelGCThreads; i++) {
4712 _survivor_plab_array[i].reset();
4713 }
4714 }
4715
4716 // Merge the per-thread plab arrays into the global survivor chunk
4717 // array which will provide the partitioning of the survivor space
4718 // for CMS initial scan and rescan.
4719 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
4720 int no_of_gc_threads) {
4721 assert(_survivor_plab_array != NULL, "Error");
4722 assert(_survivor_chunk_array != NULL, "Error");
4723 assert(_collectorState == FinalMarking ||
4724 (CMSParallelInitialMarkEnabled && _collectorState == InitialMarking), "Error");
4725 for (int j = 0; j < no_of_gc_threads; j++) {
4726 _cursor[j] = 0;
4727 }
4728 HeapWord* top = surv->top();
4729 size_t i;
4730 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
4731 HeapWord* min_val = top; // Higher than any PLAB address
4732 uint min_tid = 0; // position of min_val this round
4733 for (int j = 0; j < no_of_gc_threads; j++) {
4734 ChunkArray* cur_sca = &_survivor_plab_array[j];
4735 if (_cursor[j] == cur_sca->end()) {
4736 continue;
4737 }
4738 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
4739 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
4740 assert(surv->used_region().contains(cur_val), "Out of bounds value");
4741 if (cur_val < min_val) {
4742 min_tid = j;
4743 min_val = cur_val;
4744 } else {
4745 assert(cur_val < top, "All recorded addresses should be less");
4746 }
4747 }
4748 // At this point min_val and min_tid are respectively
4749 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
4750 // and the thread (j) that witnesses that address.
4751 // We record this address in the _survivor_chunk_array[i]
4752 // and increment _cursor[min_tid] prior to the next round i.
4753 if (min_val == top) {
4754 break;
4755 }
4756 _survivor_chunk_array[i] = min_val;
4757 _cursor[min_tid]++;
4758 }
4759 // We are all done; record the size of the _survivor_chunk_array
4760 _survivor_chunk_index = i; // exclusive: [0, i)
4761 log_trace(gc, survivor)(" (Survivor:" SIZE_FORMAT "chunks) ", i);
4762 // Verify that we used up all the recorded entries
4763 #ifdef ASSERT
4764 size_t total = 0;
4765 for (int j = 0; j < no_of_gc_threads; j++) {
4766 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
4767 total += _cursor[j];
4768 }
4769 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
4770 // Check that the merged array is in sorted order
4771 if (total > 0) {
4772 for (size_t i = 0; i < total - 1; i++) {
4773 log_develop_trace(gc, survivor)(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
4774 i, p2i(_survivor_chunk_array[i]));
4775 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
4776 "Not sorted");
4777 }
4778 }
4779 #endif // ASSERT
4780 }
4781
4782 // Set up the space's par_seq_tasks structure for work claiming
4783 // for parallel initial scan and rescan of young gen.
4784 // See ParRescanTask where this is currently used.
4785 void
4786 CMSCollector::
4787 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
4788 assert(n_threads > 0, "Unexpected n_threads argument");
4789
4790 // Eden space
4791 if (!_young_gen->eden()->is_empty()) {
4792 SequentialSubTasksDone* pst = _young_gen->eden()->par_seq_tasks();
4793 assert(!pst->valid(), "Clobbering existing data?");
4794 // Each valid entry in [0, _eden_chunk_index) represents a task.
4795 size_t n_tasks = _eden_chunk_index + 1;
4796 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
4797 // Sets the condition for completion of the subtask (how many threads
4798 // need to finish in order to be done).
4799 pst->set_n_threads(n_threads);
4800 pst->set_n_tasks((int)n_tasks);
4801 }
4802
4803 // Merge the survivor plab arrays into _survivor_chunk_array
4804 if (_survivor_plab_array != NULL) {
4805 merge_survivor_plab_arrays(_young_gen->from(), n_threads);
4806 } else {
4807 assert(_survivor_chunk_index == 0, "Error");
4808 }
4809
4810 // To space
4811 {
4812 SequentialSubTasksDone* pst = _young_gen->to()->par_seq_tasks();
4813 assert(!pst->valid(), "Clobbering existing data?");
4814 // Sets the condition for completion of the subtask (how many threads
4815 // need to finish in order to be done).
4816 pst->set_n_threads(n_threads);
4817 pst->set_n_tasks(1);
4818 assert(pst->valid(), "Error");
4819 }
4820
4821 // From space
4822 {
4823 SequentialSubTasksDone* pst = _young_gen->from()->par_seq_tasks();
4824 assert(!pst->valid(), "Clobbering existing data?");
4825 size_t n_tasks = _survivor_chunk_index + 1;
4826 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
4827 // Sets the condition for completion of the subtask (how many threads
4828 // need to finish in order to be done).
4829 pst->set_n_threads(n_threads);
4830 pst->set_n_tasks((int)n_tasks);
4831 assert(pst->valid(), "Error");
4832 }
4833 }
4834
4835 // Parallel version of remark
4836 void CMSCollector::do_remark_parallel() {
4837 GenCollectedHeap* gch = GenCollectedHeap::heap();
4838 WorkGang* workers = gch->workers();
4839 assert(workers != NULL, "Need parallel worker threads.");
4840 // Choose to use the number of GC workers most recently set
4841 // into "active_workers".
4842 uint n_workers = workers->active_workers();
4843
4844 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4845
4846 StrongRootsScope srs(n_workers);
4847
4848 CMSParRemarkTask tsk(this, cms_space, n_workers, workers, task_queues(), &srs);
4849
4850 // We won't be iterating over the cards in the card table updating
4851 // the younger_gen cards, so we shouldn't call the following else
4852 // the verification code as well as subsequent younger_refs_iterate
4853 // code would get confused. XXX
4854 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
4855
4856 // The young gen rescan work will not be done as part of
4857 // process_roots (which currently doesn't know how to
4858 // parallelize such a scan), but rather will be broken up into
4859 // a set of parallel tasks (via the sampling that the [abortable]
4860 // preclean phase did of eden, plus the [two] tasks of
4861 // scanning the [two] survivor spaces. Further fine-grain
4862 // parallelization of the scanning of the survivor spaces
4863 // themselves, and of precleaning of the young gen itself
4864 // is deferred to the future.
4865 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
4866
4867 // The dirty card rescan work is broken up into a "sequence"
4868 // of parallel tasks (per constituent space) that are dynamically
4869 // claimed by the parallel threads.
4870 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
4871
4872 // It turns out that even when we're using 1 thread, doing the work in a
4873 // separate thread causes wide variance in run times. We can't help this
4874 // in the multi-threaded case, but we special-case n=1 here to get
4875 // repeatable measurements of the 1-thread overhead of the parallel code.
4876 if (n_workers > 1) {
4877 // Make refs discovery MT-safe, if it isn't already: it may not
4878 // necessarily be so, since it's possible that we are doing
4879 // ST marking.
4880 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
4881 workers->run_task(&tsk);
4882 } else {
4883 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4884 tsk.work(0);
4885 }
4886
4887 // restore, single-threaded for now, any preserved marks
4888 // as a result of work_q overflow
4889 restore_preserved_marks_if_any();
4890 }
4891
4892 // Non-parallel version of remark
4893 void CMSCollector::do_remark_non_parallel() {
4894 ResourceMark rm;
4895 HandleMark hm;
4896 GenCollectedHeap* gch = GenCollectedHeap::heap();
4897 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
4898
4899 MarkRefsIntoAndScanClosure
4900 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
4901 &_markStack, this,
4902 false /* should_yield */, false /* not precleaning */);
4903 MarkFromDirtyCardsClosure
4904 markFromDirtyCardsClosure(this, _span,
4905 NULL, // space is set further below
4906 &_markBitMap, &_markStack, &mrias_cl);
4907 {
4908 GCTraceTime(Trace, gc, phases) t("Grey Object Rescan", _gc_timer_cm);
4909 // Iterate over the dirty cards, setting the corresponding bits in the
4910 // mod union table.
4911 {
4912 ModUnionClosure modUnionClosure(&_modUnionTable);
4913 _ct->ct_bs()->dirty_card_iterate(
4914 _cmsGen->used_region(),
4915 &modUnionClosure);
4916 }
4917 // Having transferred these marks into the modUnionTable, we just need
4918 // to rescan the marked objects on the dirty cards in the modUnionTable.
4919 // The initial marking may have been done during an asynchronous
4920 // collection so there may be dirty bits in the mod-union table.
4921 const int alignment =
4922 CardTableModRefBS::card_size * BitsPerWord;
4923 {
4924 // ... First handle dirty cards in CMS gen
4925 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
4926 MemRegion ur = _cmsGen->used_region();
4927 HeapWord* lb = ur.start();
4928 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
4929 MemRegion cms_span(lb, ub);
4930 _modUnionTable.dirty_range_iterate_clear(cms_span,
4931 &markFromDirtyCardsClosure);
4932 verify_work_stacks_empty();
4933 log_trace(gc)(" (re-scanned " SIZE_FORMAT " dirty cards in cms gen) ", markFromDirtyCardsClosure.num_dirty_cards());
4934 }
4935 }
4936 if (VerifyDuringGC &&
4937 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
4938 HandleMark hm; // Discard invalid handles created during verification
4939 Universe::verify();
4940 }
4941 {
4942 GCTraceTime(Trace, gc, phases) t("Root Rescan", _gc_timer_cm);
4943
4944 verify_work_stacks_empty();
4945
4946 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
4947 StrongRootsScope srs(1);
4948
4949 gch->gen_process_roots(&srs,
4950 GenCollectedHeap::OldGen,
4951 true, // young gen as roots
4952 GenCollectedHeap::ScanningOption(roots_scanning_options()),
4953 should_unload_classes(),
4954 &mrias_cl,
4955 NULL,
4956 NULL); // The dirty klasses will be handled below
4957
4958 assert(should_unload_classes()
4959 || (roots_scanning_options() & GenCollectedHeap::SO_AllCodeCache),
4960 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
4961 }
4962
4963 {
4964 GCTraceTime(Trace, gc, phases) t("Visit Unhandled CLDs", _gc_timer_cm);
4965
4966 verify_work_stacks_empty();
4967
4968 // Scan all class loader data objects that might have been introduced
4969 // during concurrent marking.
4970 ResourceMark rm;
4971 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
4972 for (int i = 0; i < array->length(); i++) {
4973 mrias_cl.do_cld_nv(array->at(i));
4974 }
4975
4976 // We don't need to keep track of new CLDs anymore.
4977 ClassLoaderDataGraph::remember_new_clds(false);
4978
4979 verify_work_stacks_empty();
4980 }
4981
4982 {
4983 GCTraceTime(Trace, gc, phases) t("Dirty Klass Scan", _gc_timer_cm);
4984
4985 verify_work_stacks_empty();
4986
4987 RemarkKlassClosure remark_klass_closure(&mrias_cl);
4988 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
4989
4990 verify_work_stacks_empty();
4991 }
4992
4993 // We might have added oops to ClassLoaderData::_handles during the
4994 // concurrent marking phase. These oops point to newly allocated objects
4995 // that are guaranteed to be kept alive. Either by the direct allocation
4996 // code, or when the young collector processes the roots. Hence,
4997 // we don't have to revisit the _handles block during the remark phase.
4998
4999 verify_work_stacks_empty();
5000 // Restore evacuated mark words, if any, used for overflow list links
5001 restore_preserved_marks_if_any();
5002
5003 verify_overflow_empty();
5004 }
5005
5006 ////////////////////////////////////////////////////////
5007 // Parallel Reference Processing Task Proxy Class
5008 ////////////////////////////////////////////////////////
5009 class AbstractGangTaskWOopQueues : public AbstractGangTask {
5010 OopTaskQueueSet* _queues;
5011 ParallelTaskTerminator _terminator;
5012 public:
5013 AbstractGangTaskWOopQueues(const char* name, OopTaskQueueSet* queues, uint n_threads) :
5014 AbstractGangTask(name), _queues(queues), _terminator(n_threads, _queues) {}
5015 ParallelTaskTerminator* terminator() { return &_terminator; }
5016 OopTaskQueueSet* queues() { return _queues; }
5017 };
5018
5019 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5020 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5021 CMSCollector* _collector;
5022 CMSBitMap* _mark_bit_map;
5023 const MemRegion _span;
5024 ProcessTask& _task;
5025
5026 public:
5027 CMSRefProcTaskProxy(ProcessTask& task,
5028 CMSCollector* collector,
5029 const MemRegion& span,
5030 CMSBitMap* mark_bit_map,
5031 AbstractWorkGang* workers,
5032 OopTaskQueueSet* task_queues):
5033 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5034 task_queues,
5035 workers->active_workers()),
5036 _task(task),
5037 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5038 {
5039 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5040 "Inconsistency in _span");
5041 }
5042
5043 OopTaskQueueSet* task_queues() { return queues(); }
5044
5045 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5046
5047 void do_work_steal(int i,
5048 CMSParDrainMarkingStackClosure* drain,
5049 CMSParKeepAliveClosure* keep_alive,
5050 int* seed);
5051
5052 virtual void work(uint worker_id);
5053 };
5054
5055 void CMSRefProcTaskProxy::work(uint worker_id) {
5056 ResourceMark rm;
5057 HandleMark hm;
5058 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5059 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5060 _mark_bit_map,
5061 work_queue(worker_id));
5062 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5063 _mark_bit_map,
5064 work_queue(worker_id));
5065 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5066 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5067 if (_task.marks_oops_alive()) {
5068 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5069 _collector->hash_seed(worker_id));
5070 }
5071 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5072 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5073 }
5074
5075 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5076 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5077 EnqueueTask& _task;
5078
5079 public:
5080 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5081 : AbstractGangTask("Enqueue reference objects in parallel"),
5082 _task(task)
5083 { }
5084
5085 virtual void work(uint worker_id)
5086 {
5087 _task.work(worker_id);
5088 }
5089 };
5090
5091 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5092 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5093 _span(span),
5094 _bit_map(bit_map),
5095 _work_queue(work_queue),
5096 _mark_and_push(collector, span, bit_map, work_queue),
5097 _low_water_mark(MIN2((work_queue->max_elems()/4),
5098 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5099 { }
5100
5101 // . see if we can share work_queues with ParNew? XXX
5102 void CMSRefProcTaskProxy::do_work_steal(int i,
5103 CMSParDrainMarkingStackClosure* drain,
5104 CMSParKeepAliveClosure* keep_alive,
5105 int* seed) {
5106 OopTaskQueue* work_q = work_queue(i);
5107 NOT_PRODUCT(int num_steals = 0;)
5108 oop obj_to_scan;
5109
5110 while (true) {
5111 // Completely finish any left over work from (an) earlier round(s)
5112 drain->trim_queue(0);
5113 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5114 (size_t)ParGCDesiredObjsFromOverflowList);
5115 // Now check if there's any work in the overflow list
5116 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5117 // only affects the number of attempts made to get work from the
5118 // overflow list and does not affect the number of workers. Just
5119 // pass ParallelGCThreads so this behavior is unchanged.
5120 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5121 work_q,
5122 ParallelGCThreads)) {
5123 // Found something in global overflow list;
5124 // not yet ready to go stealing work from others.
5125 // We'd like to assert(work_q->size() != 0, ...)
5126 // because we just took work from the overflow list,
5127 // but of course we can't, since all of that might have
5128 // been already stolen from us.
5129 continue;
5130 }
5131 // Verify that we have no work before we resort to stealing
5132 assert(work_q->size() == 0, "Have work, shouldn't steal");
5133 // Try to steal from other queues that have work
5134 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5135 NOT_PRODUCT(num_steals++;)
5136 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5137 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5138 // Do scanning work
5139 obj_to_scan->oop_iterate(keep_alive);
5140 // Loop around, finish this work, and try to steal some more
5141 } else if (terminator()->offer_termination()) {
5142 break; // nirvana from the infinite cycle
5143 }
5144 }
5145 log_develop_trace(gc, task)("\t(%d: stole %d oops)", i, num_steals);
5146 }
5147
5148 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5149 {
5150 GenCollectedHeap* gch = GenCollectedHeap::heap();
5151 WorkGang* workers = gch->workers();
5152 assert(workers != NULL, "Need parallel worker threads.");
5153 CMSRefProcTaskProxy rp_task(task, &_collector,
5154 _collector.ref_processor()->span(),
5155 _collector.markBitMap(),
5156 workers, _collector.task_queues());
5157 workers->run_task(&rp_task);
5158 }
5159
5160 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5161 {
5162
5163 GenCollectedHeap* gch = GenCollectedHeap::heap();
5164 WorkGang* workers = gch->workers();
5165 assert(workers != NULL, "Need parallel worker threads.");
5166 CMSRefEnqueueTaskProxy enq_task(task);
5167 workers->run_task(&enq_task);
5168 }
5169
5170 void CMSCollector::refProcessingWork() {
5171 ResourceMark rm;
5172 HandleMark hm;
5173
5174 ReferenceProcessor* rp = ref_processor();
5175 assert(rp->span().equals(_span), "Spans should be equal");
5176 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5177 // Process weak references.
5178 rp->setup_policy(false);
5179 verify_work_stacks_empty();
5180
5181 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5182 &_markStack, false /* !preclean */);
5183 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5184 _span, &_markBitMap, &_markStack,
5185 &cmsKeepAliveClosure, false /* !preclean */);
5186 {
5187 GCTraceTime(Debug, gc, phases) t("Reference Processing", _gc_timer_cm);
5188
5189 ReferenceProcessorStats stats;
5190 if (rp->processing_is_mt()) {
5191 // Set the degree of MT here. If the discovery is done MT, there
5192 // may have been a different number of threads doing the discovery
5193 // and a different number of discovered lists may have Ref objects.
5194 // That is OK as long as the Reference lists are balanced (see
5195 // balance_all_queues() and balance_queues()).
5196 GenCollectedHeap* gch = GenCollectedHeap::heap();
5197 uint active_workers = ParallelGCThreads;
5198 WorkGang* workers = gch->workers();
5199 if (workers != NULL) {
5200 active_workers = workers->active_workers();
5201 // The expectation is that active_workers will have already
5202 // been set to a reasonable value. If it has not been set,
5203 // investigate.
5204 assert(active_workers > 0, "Should have been set during scavenge");
5205 }
5206 rp->set_active_mt_degree(active_workers);
5207 CMSRefProcTaskExecutor task_executor(*this);
5208 stats = rp->process_discovered_references(&_is_alive_closure,
5209 &cmsKeepAliveClosure,
5210 &cmsDrainMarkingStackClosure,
5211 &task_executor,
5212 _gc_timer_cm);
5213 } else {
5214 stats = rp->process_discovered_references(&_is_alive_closure,
5215 &cmsKeepAliveClosure,
5216 &cmsDrainMarkingStackClosure,
5217 NULL,
5218 _gc_timer_cm);
5219 }
5220 _gc_tracer_cm->report_gc_reference_stats(stats);
5221
5222 }
5223
5224 // This is the point where the entire marking should have completed.
5225 verify_work_stacks_empty();
5226
5227 if (should_unload_classes()) {
5228 {
5229 GCTraceTime(Debug, gc, phases) t("Class Unloading", _gc_timer_cm);
5230
5231 // Unload classes and purge the SystemDictionary.
5232 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5233
5234 // Unload nmethods.
5235 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5236
5237 // Prune dead klasses from subklass/sibling/implementor lists.
5238 Klass::clean_weak_klass_links(&_is_alive_closure);
5239 }
5240
5241 {
5242 GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", _gc_timer_cm);
5243 // Clean up unreferenced symbols in symbol table.
5244 SymbolTable::unlink();
5245 }
5246
5247 {
5248 GCTraceTime(Debug, gc, phases) t("Scrub String Table", _gc_timer_cm);
5249 // Delete entries for dead interned strings.
5250 StringTable::unlink(&_is_alive_closure);
5251 }
5252 }
5253
5254
5255 // Restore any preserved marks as a result of mark stack or
5256 // work queue overflow
5257 restore_preserved_marks_if_any(); // done single-threaded for now
5258
5259 rp->set_enqueuing_is_done(true);
5260 if (rp->processing_is_mt()) {
5261 rp->balance_all_queues();
5262 CMSRefProcTaskExecutor task_executor(*this);
5263 rp->enqueue_discovered_references(&task_executor);
5264 } else {
5265 rp->enqueue_discovered_references(NULL);
5266 }
5267 rp->verify_no_references_recorded();
5268 assert(!rp->discovery_enabled(), "should have been disabled");
5269 }
5270
5271 #ifndef PRODUCT
5272 void CMSCollector::check_correct_thread_executing() {
5273 Thread* t = Thread::current();
5274 // Only the VM thread or the CMS thread should be here.
5275 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
5276 "Unexpected thread type");
5277 // If this is the vm thread, the foreground process
5278 // should not be waiting. Note that _foregroundGCIsActive is
5279 // true while the foreground collector is waiting.
5280 if (_foregroundGCShouldWait) {
5281 // We cannot be the VM thread
5282 assert(t->is_ConcurrentGC_thread(),
5283 "Should be CMS thread");
5284 } else {
5285 // We can be the CMS thread only if we are in a stop-world
5286 // phase of CMS collection.
5287 if (t->is_ConcurrentGC_thread()) {
5288 assert(_collectorState == InitialMarking ||
5289 _collectorState == FinalMarking,
5290 "Should be a stop-world phase");
5291 // The CMS thread should be holding the CMS_token.
5292 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5293 "Potential interference with concurrently "
5294 "executing VM thread");
5295 }
5296 }
5297 }
5298 #endif
5299
5300 void CMSCollector::sweep() {
5301 assert(_collectorState == Sweeping, "just checking");
5302 check_correct_thread_executing();
5303 verify_work_stacks_empty();
5304 verify_overflow_empty();
5305 increment_sweep_count();
5306 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
5307
5308 _inter_sweep_timer.stop();
5309 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
5310
5311 assert(!_intra_sweep_timer.is_active(), "Should not be active");
5312 _intra_sweep_timer.reset();
5313 _intra_sweep_timer.start();
5314 {
5315 GCTraceCPUTime tcpu;
5316 CMSPhaseAccounting pa(this, "Concurrent Sweep");
5317 // First sweep the old gen
5318 {
5319 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
5320 bitMapLock());
5321 sweepWork(_cmsGen);
5322 }
5323
5324 // Update Universe::_heap_*_at_gc figures.
5325 // We need all the free list locks to make the abstract state
5326 // transition from Sweeping to Resetting. See detailed note
5327 // further below.
5328 {
5329 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
5330 // Update heap occupancy information which is used as
5331 // input to soft ref clearing policy at the next gc.
5332 Universe::update_heap_info_at_gc();
5333 _collectorState = Resizing;
5334 }
5335 }
5336 verify_work_stacks_empty();
5337 verify_overflow_empty();
5338
5339 if (should_unload_classes()) {
5340 // Delay purge to the beginning of the next safepoint. Metaspace::contains
5341 // requires that the virtual spaces are stable and not deleted.
5342 ClassLoaderDataGraph::set_should_purge(true);
5343 }
5344
5345 _intra_sweep_timer.stop();
5346 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
5347
5348 _inter_sweep_timer.reset();
5349 _inter_sweep_timer.start();
5350
5351 // We need to use a monotonically non-decreasing time in ms
5352 // or we will see time-warp warnings and os::javaTimeMillis()
5353 // does not guarantee monotonicity.
5354 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
5355 update_time_of_last_gc(now);
5356
5357 // NOTE on abstract state transitions:
5358 // Mutators allocate-live and/or mark the mod-union table dirty
5359 // based on the state of the collection. The former is done in
5360 // the interval [Marking, Sweeping] and the latter in the interval
5361 // [Marking, Sweeping). Thus the transitions into the Marking state
5362 // and out of the Sweeping state must be synchronously visible
5363 // globally to the mutators.
5364 // The transition into the Marking state happens with the world
5365 // stopped so the mutators will globally see it. Sweeping is
5366 // done asynchronously by the background collector so the transition
5367 // from the Sweeping state to the Resizing state must be done
5368 // under the freelistLock (as is the check for whether to
5369 // allocate-live and whether to dirty the mod-union table).
5370 assert(_collectorState == Resizing, "Change of collector state to"
5371 " Resizing must be done under the freelistLocks (plural)");
5372
5373 // Now that sweeping has been completed, we clear
5374 // the incremental_collection_failed flag,
5375 // thus inviting a younger gen collection to promote into
5376 // this generation. If such a promotion may still fail,
5377 // the flag will be set again when a young collection is
5378 // attempted.
5379 GenCollectedHeap* gch = GenCollectedHeap::heap();
5380 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
5381 gch->update_full_collections_completed(_collection_count_start);
5382 }
5383
5384 // FIX ME!!! Looks like this belongs in CFLSpace, with
5385 // CMSGen merely delegating to it.
5386 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
5387 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
5388 HeapWord* minAddr = _cmsSpace->bottom();
5389 HeapWord* largestAddr =
5390 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
5391 if (largestAddr == NULL) {
5392 // The dictionary appears to be empty. In this case
5393 // try to coalesce at the end of the heap.
5394 largestAddr = _cmsSpace->end();
5395 }
5396 size_t largestOffset = pointer_delta(largestAddr, minAddr);
5397 size_t nearLargestOffset =
5398 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
5399 log_debug(gc, freelist)("CMS: Large Block: " PTR_FORMAT "; Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
5400 p2i(largestAddr), p2i(_cmsSpace->nearLargestChunk()), p2i(minAddr + nearLargestOffset));
5401 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
5402 }
5403
5404 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
5405 return addr >= _cmsSpace->nearLargestChunk();
5406 }
5407
5408 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
5409 return _cmsSpace->find_chunk_at_end();
5410 }
5411
5412 void ConcurrentMarkSweepGeneration::update_gc_stats(Generation* current_generation,
5413 bool full) {
5414 // If the young generation has been collected, gather any statistics
5415 // that are of interest at this point.
5416 bool current_is_young = GenCollectedHeap::heap()->is_young_gen(current_generation);
5417 if (!full && current_is_young) {
5418 // Gather statistics on the young generation collection.
5419 collector()->stats().record_gc0_end(used());
5420 }
5421 }
5422
5423 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* old_gen) {
5424 // We iterate over the space(s) underlying this generation,
5425 // checking the mark bit map to see if the bits corresponding
5426 // to specific blocks are marked or not. Blocks that are
5427 // marked are live and are not swept up. All remaining blocks
5428 // are swept up, with coalescing on-the-fly as we sweep up
5429 // contiguous free and/or garbage blocks:
5430 // We need to ensure that the sweeper synchronizes with allocators
5431 // and stop-the-world collectors. In particular, the following
5432 // locks are used:
5433 // . CMS token: if this is held, a stop the world collection cannot occur
5434 // . freelistLock: if this is held no allocation can occur from this
5435 // generation by another thread
5436 // . bitMapLock: if this is held, no other thread can access or update
5437 //
5438
5439 // Note that we need to hold the freelistLock if we use
5440 // block iterate below; else the iterator might go awry if
5441 // a mutator (or promotion) causes block contents to change
5442 // (for instance if the allocator divvies up a block).
5443 // If we hold the free list lock, for all practical purposes
5444 // young generation GC's can't occur (they'll usually need to
5445 // promote), so we might as well prevent all young generation
5446 // GC's while we do a sweeping step. For the same reason, we might
5447 // as well take the bit map lock for the entire duration
5448
5449 // check that we hold the requisite locks
5450 assert(have_cms_token(), "Should hold cms token");
5451 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), "Should possess CMS token to sweep");
5452 assert_lock_strong(old_gen->freelistLock());
5453 assert_lock_strong(bitMapLock());
5454
5455 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
5456 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
5457 old_gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
5458 _inter_sweep_estimate.padded_average(),
5459 _intra_sweep_estimate.padded_average());
5460 old_gen->setNearLargestChunk();
5461
5462 {
5463 SweepClosure sweepClosure(this, old_gen, &_markBitMap, CMSYield);
5464 old_gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
5465 // We need to free-up/coalesce garbage/blocks from a
5466 // co-terminal free run. This is done in the SweepClosure
5467 // destructor; so, do not remove this scope, else the
5468 // end-of-sweep-census below will be off by a little bit.
5469 }
5470 old_gen->cmsSpace()->sweep_completed();
5471 old_gen->cmsSpace()->endSweepFLCensus(sweep_count());
5472 if (should_unload_classes()) { // unloaded classes this cycle,
5473 _concurrent_cycles_since_last_unload = 0; // ... reset count
5474 } else { // did not unload classes,
5475 _concurrent_cycles_since_last_unload++; // ... increment count
5476 }
5477 }
5478
5479 // Reset CMS data structures (for now just the marking bit map)
5480 // preparatory for the next cycle.
5481 void CMSCollector::reset_concurrent() {
5482 CMSTokenSyncWithLocks ts(true, bitMapLock());
5483
5484 // If the state is not "Resetting", the foreground thread
5485 // has done a collection and the resetting.
5486 if (_collectorState != Resetting) {
5487 assert(_collectorState == Idling, "The state should only change"
5488 " because the foreground collector has finished the collection");
5489 return;
5490 }
5491
5492 {
5493 // Clear the mark bitmap (no grey objects to start with)
5494 // for the next cycle.
5495 GCTraceCPUTime tcpu;
5496 CMSPhaseAccounting cmspa(this, "Concurrent Reset");
5497
5498 HeapWord* curAddr = _markBitMap.startWord();
5499 while (curAddr < _markBitMap.endWord()) {
5500 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
5501 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
5502 _markBitMap.clear_large_range(chunk);
5503 if (ConcurrentMarkSweepThread::should_yield() &&
5504 !foregroundGCIsActive() &&
5505 CMSYield) {
5506 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5507 "CMS thread should hold CMS token");
5508 assert_lock_strong(bitMapLock());
5509 bitMapLock()->unlock();
5510 ConcurrentMarkSweepThread::desynchronize(true);
5511 stopTimer();
5512 incrementYields();
5513
5514 // See the comment in coordinator_yield()
5515 for (unsigned i = 0; i < CMSYieldSleepCount &&
5516 ConcurrentMarkSweepThread::should_yield() &&
5517 !CMSCollector::foregroundGCIsActive(); ++i) {
5518 os::sleep(Thread::current(), 1, false);
5519 }
5520
5521 ConcurrentMarkSweepThread::synchronize(true);
5522 bitMapLock()->lock_without_safepoint_check();
5523 startTimer();
5524 }
5525 curAddr = chunk.end();
5526 }
5527 // A successful mostly concurrent collection has been done.
5528 // Because only the full (i.e., concurrent mode failure) collections
5529 // are being measured for gc overhead limits, clean the "near" flag
5530 // and count.
5531 size_policy()->reset_gc_overhead_limit_count();
5532 _collectorState = Idling;
5533 }
5534
5535 register_gc_end();
5536 }
5537
5538 // Same as above but for STW paths
5539 void CMSCollector::reset_stw() {
5540 // already have the lock
5541 assert(_collectorState == Resetting, "just checking");
5542 assert_lock_strong(bitMapLock());
5543 GCIdMarkAndRestore gc_id_mark(_cmsThread->gc_id());
5544 _markBitMap.clear_all();
5545 _collectorState = Idling;
5546 register_gc_end();
5547 }
5548
5549 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
5550 GCTraceCPUTime tcpu;
5551 TraceCollectorStats tcs(counters());
5552
5553 switch (op) {
5554 case CMS_op_checkpointRootsInitial: {
5555 GCTraceTime(Info, gc) t("Pause Initial Mark", NULL, GCCause::_no_gc, true);
5556 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5557 checkpointRootsInitial();
5558 break;
5559 }
5560 case CMS_op_checkpointRootsFinal: {
5561 GCTraceTime(Info, gc) t("Pause Remark", NULL, GCCause::_no_gc, true);
5562 SvcGCMarker sgcm(SvcGCMarker::OTHER);
5563 checkpointRootsFinal();
5564 break;
5565 }
5566 default:
5567 fatal("No such CMS_op");
5568 }
5569 }
5570
5571 #ifndef PRODUCT
5572 size_t const CMSCollector::skip_header_HeapWords() {
5573 return FreeChunk::header_size();
5574 }
5575
5576 // Try and collect here conditions that should hold when
5577 // CMS thread is exiting. The idea is that the foreground GC
5578 // thread should not be blocked if it wants to terminate
5579 // the CMS thread and yet continue to run the VM for a while
5580 // after that.
5581 void CMSCollector::verify_ok_to_terminate() const {
5582 assert(Thread::current()->is_ConcurrentGC_thread(),
5583 "should be called by CMS thread");
5584 assert(!_foregroundGCShouldWait, "should be false");
5585 // We could check here that all the various low-level locks
5586 // are not held by the CMS thread, but that is overkill; see
5587 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
5588 // is checked.
5589 }
5590 #endif
5591
5592 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
5593 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
5594 "missing Printezis mark?");
5595 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5596 size_t size = pointer_delta(nextOneAddr + 1, addr);
5597 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5598 "alignment problem");
5599 assert(size >= 3, "Necessary for Printezis marks to work");
5600 return size;
5601 }
5602
5603 // A variant of the above (block_size_using_printezis_bits()) except
5604 // that we return 0 if the P-bits are not yet set.
5605 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
5606 if (_markBitMap.isMarked(addr + 1)) {
5607 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
5608 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
5609 size_t size = pointer_delta(nextOneAddr + 1, addr);
5610 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
5611 "alignment problem");
5612 assert(size >= 3, "Necessary for Printezis marks to work");
5613 return size;
5614 }
5615 return 0;
5616 }
5617
5618 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
5619 size_t sz = 0;
5620 oop p = (oop)addr;
5621 if (p->klass_or_null() != NULL) {
5622 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
5623 } else {
5624 sz = block_size_using_printezis_bits(addr);
5625 }
5626 assert(sz > 0, "size must be nonzero");
5627 HeapWord* next_block = addr + sz;
5628 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
5629 CardTableModRefBS::card_size);
5630 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
5631 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
5632 "must be different cards");
5633 return next_card;
5634 }
5635
5636
5637 // CMS Bit Map Wrapper /////////////////////////////////////////
5638
5639 // Construct a CMS bit map infrastructure, but don't create the
5640 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
5641 // further below.
5642 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
5643 _bm(),
5644 _shifter(shifter),
5645 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true,
5646 Monitor::_safepoint_check_sometimes) : NULL)
5647 {
5648 _bmStartWord = 0;
5649 _bmWordSize = 0;
5650 }
5651
5652 bool CMSBitMap::allocate(MemRegion mr) {
5653 _bmStartWord = mr.start();
5654 _bmWordSize = mr.word_size();
5655 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
5656 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
5657 if (!brs.is_reserved()) {
5658 log_warning(gc)("CMS bit map allocation failure");
5659 return false;
5660 }
5661 // For now we'll just commit all of the bit map up front.
5662 // Later on we'll try to be more parsimonious with swap.
5663 if (!_virtual_space.initialize(brs, brs.size())) {
5664 log_warning(gc)("CMS bit map backing store failure");
5665 return false;
5666 }
5667 assert(_virtual_space.committed_size() == brs.size(),
5668 "didn't reserve backing store for all of CMS bit map?");
5669 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
5670 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
5671 _bmWordSize, "inconsistency in bit map sizing");
5672 _bm.set_size(_bmWordSize >> _shifter);
5673
5674 // bm.clear(); // can we rely on getting zero'd memory? verify below
5675 assert(isAllClear(),
5676 "Expected zero'd memory from ReservedSpace constructor");
5677 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
5678 "consistency check");
5679 return true;
5680 }
5681
5682 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
5683 HeapWord *next_addr, *end_addr, *last_addr;
5684 assert_locked();
5685 assert(covers(mr), "out-of-range error");
5686 // XXX assert that start and end are appropriately aligned
5687 for (next_addr = mr.start(), end_addr = mr.end();
5688 next_addr < end_addr; next_addr = last_addr) {
5689 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
5690 last_addr = dirty_region.end();
5691 if (!dirty_region.is_empty()) {
5692 cl->do_MemRegion(dirty_region);
5693 } else {
5694 assert(last_addr == end_addr, "program logic");
5695 return;
5696 }
5697 }
5698 }
5699
5700 void CMSBitMap::print_on_error(outputStream* st, const char* prefix) const {
5701 _bm.print_on_error(st, prefix);
5702 }
5703
5704 #ifndef PRODUCT
5705 void CMSBitMap::assert_locked() const {
5706 CMSLockVerifier::assert_locked(lock());
5707 }
5708
5709 bool CMSBitMap::covers(MemRegion mr) const {
5710 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
5711 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
5712 "size inconsistency");
5713 return (mr.start() >= _bmStartWord) &&
5714 (mr.end() <= endWord());
5715 }
5716
5717 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
5718 return (start >= _bmStartWord && (start + size) <= endWord());
5719 }
5720
5721 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
5722 // verify that there are no 1 bits in the interval [left, right)
5723 FalseBitMapClosure falseBitMapClosure;
5724 iterate(&falseBitMapClosure, left, right);
5725 }
5726
5727 void CMSBitMap::region_invariant(MemRegion mr)
5728 {
5729 assert_locked();
5730 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
5731 assert(!mr.is_empty(), "unexpected empty region");
5732 assert(covers(mr), "mr should be covered by bit map");
5733 // convert address range into offset range
5734 size_t start_ofs = heapWordToOffset(mr.start());
5735 // Make sure that end() is appropriately aligned
5736 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
5737 (1 << (_shifter+LogHeapWordSize))),
5738 "Misaligned mr.end()");
5739 size_t end_ofs = heapWordToOffset(mr.end());
5740 assert(end_ofs > start_ofs, "Should mark at least one bit");
5741 }
5742
5743 #endif
5744
5745 bool CMSMarkStack::allocate(size_t size) {
5746 // allocate a stack of the requisite depth
5747 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5748 size * sizeof(oop)));
5749 if (!rs.is_reserved()) {
5750 log_warning(gc)("CMSMarkStack allocation failure");
5751 return false;
5752 }
5753 if (!_virtual_space.initialize(rs, rs.size())) {
5754 log_warning(gc)("CMSMarkStack backing store failure");
5755 return false;
5756 }
5757 assert(_virtual_space.committed_size() == rs.size(),
5758 "didn't reserve backing store for all of CMS stack?");
5759 _base = (oop*)(_virtual_space.low());
5760 _index = 0;
5761 _capacity = size;
5762 NOT_PRODUCT(_max_depth = 0);
5763 return true;
5764 }
5765
5766 // XXX FIX ME !!! In the MT case we come in here holding a
5767 // leaf lock. For printing we need to take a further lock
5768 // which has lower rank. We need to recalibrate the two
5769 // lock-ranks involved in order to be able to print the
5770 // messages below. (Or defer the printing to the caller.
5771 // For now we take the expedient path of just disabling the
5772 // messages for the problematic case.)
5773 void CMSMarkStack::expand() {
5774 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
5775 if (_capacity == MarkStackSizeMax) {
5776 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled) {
5777 // We print a warning message only once per CMS cycle.
5778 log_debug(gc)(" (benign) Hit CMSMarkStack max size limit");
5779 }
5780 return;
5781 }
5782 // Double capacity if possible
5783 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
5784 // Do not give up existing stack until we have managed to
5785 // get the double capacity that we desired.
5786 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
5787 new_capacity * sizeof(oop)));
5788 if (rs.is_reserved()) {
5789 // Release the backing store associated with old stack
5790 _virtual_space.release();
5791 // Reinitialize virtual space for new stack
5792 if (!_virtual_space.initialize(rs, rs.size())) {
5793 fatal("Not enough swap for expanded marking stack");
5794 }
5795 _base = (oop*)(_virtual_space.low());
5796 _index = 0;
5797 _capacity = new_capacity;
5798 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled) {
5799 // Failed to double capacity, continue;
5800 // we print a detail message only once per CMS cycle.
5801 log_debug(gc)(" (benign) Failed to expand marking stack from " SIZE_FORMAT "K to " SIZE_FORMAT "K",
5802 _capacity / K, new_capacity / K);
5803 }
5804 }
5805
5806
5807 // Closures
5808 // XXX: there seems to be a lot of code duplication here;
5809 // should refactor and consolidate common code.
5810
5811 // This closure is used to mark refs into the CMS generation in
5812 // the CMS bit map. Called at the first checkpoint. This closure
5813 // assumes that we do not need to re-mark dirty cards; if the CMS
5814 // generation on which this is used is not an oldest
5815 // generation then this will lose younger_gen cards!
5816
5817 MarkRefsIntoClosure::MarkRefsIntoClosure(
5818 MemRegion span, CMSBitMap* bitMap):
5819 _span(span),
5820 _bitMap(bitMap)
5821 {
5822 assert(ref_processor() == NULL, "deliberately left NULL");
5823 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5824 }
5825
5826 void MarkRefsIntoClosure::do_oop(oop obj) {
5827 // if p points into _span, then mark corresponding bit in _markBitMap
5828 assert(obj->is_oop(), "expected an oop");
5829 HeapWord* addr = (HeapWord*)obj;
5830 if (_span.contains(addr)) {
5831 // this should be made more efficient
5832 _bitMap->mark(addr);
5833 }
5834 }
5835
5836 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5837 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
5838
5839 ParMarkRefsIntoClosure::ParMarkRefsIntoClosure(
5840 MemRegion span, CMSBitMap* bitMap):
5841 _span(span),
5842 _bitMap(bitMap)
5843 {
5844 assert(ref_processor() == NULL, "deliberately left NULL");
5845 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
5846 }
5847
5848 void ParMarkRefsIntoClosure::do_oop(oop obj) {
5849 // if p points into _span, then mark corresponding bit in _markBitMap
5850 assert(obj->is_oop(), "expected an oop");
5851 HeapWord* addr = (HeapWord*)obj;
5852 if (_span.contains(addr)) {
5853 // this should be made more efficient
5854 _bitMap->par_mark(addr);
5855 }
5856 }
5857
5858 void ParMarkRefsIntoClosure::do_oop(oop* p) { ParMarkRefsIntoClosure::do_oop_work(p); }
5859 void ParMarkRefsIntoClosure::do_oop(narrowOop* p) { ParMarkRefsIntoClosure::do_oop_work(p); }
5860
5861 // A variant of the above, used for CMS marking verification.
5862 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
5863 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
5864 _span(span),
5865 _verification_bm(verification_bm),
5866 _cms_bm(cms_bm)
5867 {
5868 assert(ref_processor() == NULL, "deliberately left NULL");
5869 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
5870 }
5871
5872 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
5873 // if p points into _span, then mark corresponding bit in _markBitMap
5874 assert(obj->is_oop(), "expected an oop");
5875 HeapWord* addr = (HeapWord*)obj;
5876 if (_span.contains(addr)) {
5877 _verification_bm->mark(addr);
5878 if (!_cms_bm->isMarked(addr)) {
5879 Log(gc, verify) log;
5880 ResourceMark rm;
5881 oop(addr)->print_on(log.error_stream());
5882 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
5883 fatal("... aborting");
5884 }
5885 }
5886 }
5887
5888 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5889 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
5890
5891 //////////////////////////////////////////////////
5892 // MarkRefsIntoAndScanClosure
5893 //////////////////////////////////////////////////
5894
5895 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
5896 ReferenceProcessor* rp,
5897 CMSBitMap* bit_map,
5898 CMSBitMap* mod_union_table,
5899 CMSMarkStack* mark_stack,
5900 CMSCollector* collector,
5901 bool should_yield,
5902 bool concurrent_precleaning):
5903 _collector(collector),
5904 _span(span),
5905 _bit_map(bit_map),
5906 _mark_stack(mark_stack),
5907 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
5908 mark_stack, concurrent_precleaning),
5909 _yield(should_yield),
5910 _concurrent_precleaning(concurrent_precleaning),
5911 _freelistLock(NULL)
5912 {
5913 // FIXME: Should initialize in base class constructor.
5914 assert(rp != NULL, "ref_processor shouldn't be NULL");
5915 set_ref_processor_internal(rp);
5916 }
5917
5918 // This closure is used to mark refs into the CMS generation at the
5919 // second (final) checkpoint, and to scan and transitively follow
5920 // the unmarked oops. It is also used during the concurrent precleaning
5921 // phase while scanning objects on dirty cards in the CMS generation.
5922 // The marks are made in the marking bit map and the marking stack is
5923 // used for keeping the (newly) grey objects during the scan.
5924 // The parallel version (Par_...) appears further below.
5925 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
5926 if (obj != NULL) {
5927 assert(obj->is_oop(), "expected an oop");
5928 HeapWord* addr = (HeapWord*)obj;
5929 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
5930 assert(_collector->overflow_list_is_empty(),
5931 "overflow list should be empty");
5932 if (_span.contains(addr) &&
5933 !_bit_map->isMarked(addr)) {
5934 // mark bit map (object is now grey)
5935 _bit_map->mark(addr);
5936 // push on marking stack (stack should be empty), and drain the
5937 // stack by applying this closure to the oops in the oops popped
5938 // from the stack (i.e. blacken the grey objects)
5939 bool res = _mark_stack->push(obj);
5940 assert(res, "Should have space to push on empty stack");
5941 do {
5942 oop new_oop = _mark_stack->pop();
5943 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
5944 assert(_bit_map->isMarked((HeapWord*)new_oop),
5945 "only grey objects on this stack");
5946 // iterate over the oops in this oop, marking and pushing
5947 // the ones in CMS heap (i.e. in _span).
5948 new_oop->oop_iterate(&_pushAndMarkClosure);
5949 // check if it's time to yield
5950 do_yield_check();
5951 } while (!_mark_stack->isEmpty() ||
5952 (!_concurrent_precleaning && take_from_overflow_list()));
5953 // if marking stack is empty, and we are not doing this
5954 // during precleaning, then check the overflow list
5955 }
5956 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
5957 assert(_collector->overflow_list_is_empty(),
5958 "overflow list was drained above");
5959
5960 assert(_collector->no_preserved_marks(),
5961 "All preserved marks should have been restored above");
5962 }
5963 }
5964
5965 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5966 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
5967
5968 void MarkRefsIntoAndScanClosure::do_yield_work() {
5969 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
5970 "CMS thread should hold CMS token");
5971 assert_lock_strong(_freelistLock);
5972 assert_lock_strong(_bit_map->lock());
5973 // relinquish the free_list_lock and bitMaplock()
5974 _bit_map->lock()->unlock();
5975 _freelistLock->unlock();
5976 ConcurrentMarkSweepThread::desynchronize(true);
5977 _collector->stopTimer();
5978 _collector->incrementYields();
5979
5980 // See the comment in coordinator_yield()
5981 for (unsigned i = 0;
5982 i < CMSYieldSleepCount &&
5983 ConcurrentMarkSweepThread::should_yield() &&
5984 !CMSCollector::foregroundGCIsActive();
5985 ++i) {
5986 os::sleep(Thread::current(), 1, false);
5987 }
5988
5989 ConcurrentMarkSweepThread::synchronize(true);
5990 _freelistLock->lock_without_safepoint_check();
5991 _bit_map->lock()->lock_without_safepoint_check();
5992 _collector->startTimer();
5993 }
5994
5995 ///////////////////////////////////////////////////////////
5996 // ParMarkRefsIntoAndScanClosure: a parallel version of
5997 // MarkRefsIntoAndScanClosure
5998 ///////////////////////////////////////////////////////////
5999 ParMarkRefsIntoAndScanClosure::ParMarkRefsIntoAndScanClosure(
6000 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6001 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6002 _span(span),
6003 _bit_map(bit_map),
6004 _work_queue(work_queue),
6005 _low_water_mark(MIN2((work_queue->max_elems()/4),
6006 ((uint)CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6007 _parPushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6008 {
6009 // FIXME: Should initialize in base class constructor.
6010 assert(rp != NULL, "ref_processor shouldn't be NULL");
6011 set_ref_processor_internal(rp);
6012 }
6013
6014 // This closure is used to mark refs into the CMS generation at the
6015 // second (final) checkpoint, and to scan and transitively follow
6016 // the unmarked oops. The marks are made in the marking bit map and
6017 // the work_queue is used for keeping the (newly) grey objects during
6018 // the scan phase whence they are also available for stealing by parallel
6019 // threads. Since the marking bit map is shared, updates are
6020 // synchronized (via CAS).
6021 void ParMarkRefsIntoAndScanClosure::do_oop(oop obj) {
6022 if (obj != NULL) {
6023 // Ignore mark word because this could be an already marked oop
6024 // that may be chained at the end of the overflow list.
6025 assert(obj->is_oop(true), "expected an oop");
6026 HeapWord* addr = (HeapWord*)obj;
6027 if (_span.contains(addr) &&
6028 !_bit_map->isMarked(addr)) {
6029 // mark bit map (object will become grey):
6030 // It is possible for several threads to be
6031 // trying to "claim" this object concurrently;
6032 // the unique thread that succeeds in marking the
6033 // object first will do the subsequent push on
6034 // to the work queue (or overflow list).
6035 if (_bit_map->par_mark(addr)) {
6036 // push on work_queue (which may not be empty), and trim the
6037 // queue to an appropriate length by applying this closure to
6038 // the oops in the oops popped from the stack (i.e. blacken the
6039 // grey objects)
6040 bool res = _work_queue->push(obj);
6041 assert(res, "Low water mark should be less than capacity?");
6042 trim_queue(_low_water_mark);
6043 } // Else, another thread claimed the object
6044 }
6045 }
6046 }
6047
6048 void ParMarkRefsIntoAndScanClosure::do_oop(oop* p) { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6049 void ParMarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { ParMarkRefsIntoAndScanClosure::do_oop_work(p); }
6050
6051 // This closure is used to rescan the marked objects on the dirty cards
6052 // in the mod union table and the card table proper.
6053 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6054 oop p, MemRegion mr) {
6055
6056 size_t size = 0;
6057 HeapWord* addr = (HeapWord*)p;
6058 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6059 assert(_span.contains(addr), "we are scanning the CMS generation");
6060 // check if it's time to yield
6061 if (do_yield_check()) {
6062 // We yielded for some foreground stop-world work,
6063 // and we have been asked to abort this ongoing preclean cycle.
6064 return 0;
6065 }
6066 if (_bitMap->isMarked(addr)) {
6067 // it's marked; is it potentially uninitialized?
6068 if (p->klass_or_null() != NULL) {
6069 // an initialized object; ignore mark word in verification below
6070 // since we are running concurrent with mutators
6071 assert(p->is_oop(true), "should be an oop");
6072 if (p->is_objArray()) {
6073 // objArrays are precisely marked; restrict scanning
6074 // to dirty cards only.
6075 size = CompactibleFreeListSpace::adjustObjectSize(
6076 p->oop_iterate_size(_scanningClosure, mr));
6077 } else {
6078 // A non-array may have been imprecisely marked; we need
6079 // to scan object in its entirety.
6080 size = CompactibleFreeListSpace::adjustObjectSize(
6081 p->oop_iterate_size(_scanningClosure));
6082 }
6083 #ifdef ASSERT
6084 size_t direct_size =
6085 CompactibleFreeListSpace::adjustObjectSize(p->size());
6086 assert(size == direct_size, "Inconsistency in size");
6087 assert(size >= 3, "Necessary for Printezis marks to work");
6088 if (!_bitMap->isMarked(addr+1)) {
6089 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6090 } else {
6091 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6092 assert(_bitMap->isMarked(addr+size-1),
6093 "inconsistent Printezis mark");
6094 }
6095 #endif // ASSERT
6096 } else {
6097 // An uninitialized object.
6098 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6099 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6100 size = pointer_delta(nextOneAddr + 1, addr);
6101 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6102 "alignment problem");
6103 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6104 // will dirty the card when the klass pointer is installed in the
6105 // object (signaling the completion of initialization).
6106 }
6107 } else {
6108 // Either a not yet marked object or an uninitialized object
6109 if (p->klass_or_null() == NULL) {
6110 // An uninitialized object, skip to the next card, since
6111 // we may not be able to read its P-bits yet.
6112 assert(size == 0, "Initial value");
6113 } else {
6114 // An object not (yet) reached by marking: we merely need to
6115 // compute its size so as to go look at the next block.
6116 assert(p->is_oop(true), "should be an oop");
6117 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6118 }
6119 }
6120 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6121 return size;
6122 }
6123
6124 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6125 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6126 "CMS thread should hold CMS token");
6127 assert_lock_strong(_freelistLock);
6128 assert_lock_strong(_bitMap->lock());
6129 // relinquish the free_list_lock and bitMaplock()
6130 _bitMap->lock()->unlock();
6131 _freelistLock->unlock();
6132 ConcurrentMarkSweepThread::desynchronize(true);
6133 _collector->stopTimer();
6134 _collector->incrementYields();
6135
6136 // See the comment in coordinator_yield()
6137 for (unsigned i = 0; i < CMSYieldSleepCount &&
6138 ConcurrentMarkSweepThread::should_yield() &&
6139 !CMSCollector::foregroundGCIsActive(); ++i) {
6140 os::sleep(Thread::current(), 1, false);
6141 }
6142
6143 ConcurrentMarkSweepThread::synchronize(true);
6144 _freelistLock->lock_without_safepoint_check();
6145 _bitMap->lock()->lock_without_safepoint_check();
6146 _collector->startTimer();
6147 }
6148
6149
6150 //////////////////////////////////////////////////////////////////
6151 // SurvivorSpacePrecleanClosure
6152 //////////////////////////////////////////////////////////////////
6153 // This (single-threaded) closure is used to preclean the oops in
6154 // the survivor spaces.
6155 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6156
6157 HeapWord* addr = (HeapWord*)p;
6158 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6159 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6160 assert(p->klass_or_null() != NULL, "object should be initialized");
6161 // an initialized object; ignore mark word in verification below
6162 // since we are running concurrent with mutators
6163 assert(p->is_oop(true), "should be an oop");
6164 // Note that we do not yield while we iterate over
6165 // the interior oops of p, pushing the relevant ones
6166 // on our marking stack.
6167 size_t size = p->oop_iterate_size(_scanning_closure);
6168 do_yield_check();
6169 // Observe that below, we do not abandon the preclean
6170 // phase as soon as we should; rather we empty the
6171 // marking stack before returning. This is to satisfy
6172 // some existing assertions. In general, it may be a
6173 // good idea to abort immediately and complete the marking
6174 // from the grey objects at a later time.
6175 while (!_mark_stack->isEmpty()) {
6176 oop new_oop = _mark_stack->pop();
6177 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6178 assert(_bit_map->isMarked((HeapWord*)new_oop),
6179 "only grey objects on this stack");
6180 // iterate over the oops in this oop, marking and pushing
6181 // the ones in CMS heap (i.e. in _span).
6182 new_oop->oop_iterate(_scanning_closure);
6183 // check if it's time to yield
6184 do_yield_check();
6185 }
6186 unsigned int after_count =
6187 GenCollectedHeap::heap()->total_collections();
6188 bool abort = (_before_count != after_count) ||
6189 _collector->should_abort_preclean();
6190 return abort ? 0 : size;
6191 }
6192
6193 void SurvivorSpacePrecleanClosure::do_yield_work() {
6194 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6195 "CMS thread should hold CMS token");
6196 assert_lock_strong(_bit_map->lock());
6197 // Relinquish the bit map lock
6198 _bit_map->lock()->unlock();
6199 ConcurrentMarkSweepThread::desynchronize(true);
6200 _collector->stopTimer();
6201 _collector->incrementYields();
6202
6203 // See the comment in coordinator_yield()
6204 for (unsigned i = 0; i < CMSYieldSleepCount &&
6205 ConcurrentMarkSweepThread::should_yield() &&
6206 !CMSCollector::foregroundGCIsActive(); ++i) {
6207 os::sleep(Thread::current(), 1, false);
6208 }
6209
6210 ConcurrentMarkSweepThread::synchronize(true);
6211 _bit_map->lock()->lock_without_safepoint_check();
6212 _collector->startTimer();
6213 }
6214
6215 // This closure is used to rescan the marked objects on the dirty cards
6216 // in the mod union table and the card table proper. In the parallel
6217 // case, although the bitMap is shared, we do a single read so the
6218 // isMarked() query is "safe".
6219 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
6220 // Ignore mark word because we are running concurrent with mutators
6221 assert(p->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(p));
6222 HeapWord* addr = (HeapWord*)p;
6223 assert(_span.contains(addr), "we are scanning the CMS generation");
6224 bool is_obj_array = false;
6225 #ifdef ASSERT
6226 if (!_parallel) {
6227 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6228 assert(_collector->overflow_list_is_empty(),
6229 "overflow list should be empty");
6230
6231 }
6232 #endif // ASSERT
6233 if (_bit_map->isMarked(addr)) {
6234 // Obj arrays are precisely marked, non-arrays are not;
6235 // so we scan objArrays precisely and non-arrays in their
6236 // entirety.
6237 if (p->is_objArray()) {
6238 is_obj_array = true;
6239 if (_parallel) {
6240 p->oop_iterate(_par_scan_closure, mr);
6241 } else {
6242 p->oop_iterate(_scan_closure, mr);
6243 }
6244 } else {
6245 if (_parallel) {
6246 p->oop_iterate(_par_scan_closure);
6247 } else {
6248 p->oop_iterate(_scan_closure);
6249 }
6250 }
6251 }
6252 #ifdef ASSERT
6253 if (!_parallel) {
6254 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6255 assert(_collector->overflow_list_is_empty(),
6256 "overflow list should be empty");
6257
6258 }
6259 #endif // ASSERT
6260 return is_obj_array;
6261 }
6262
6263 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
6264 MemRegion span,
6265 CMSBitMap* bitMap, CMSMarkStack* markStack,
6266 bool should_yield, bool verifying):
6267 _collector(collector),
6268 _span(span),
6269 _bitMap(bitMap),
6270 _mut(&collector->_modUnionTable),
6271 _markStack(markStack),
6272 _yield(should_yield),
6273 _skipBits(0)
6274 {
6275 assert(_markStack->isEmpty(), "stack should be empty");
6276 _finger = _bitMap->startWord();
6277 _threshold = _finger;
6278 assert(_collector->_restart_addr == NULL, "Sanity check");
6279 assert(_span.contains(_finger), "Out of bounds _finger?");
6280 DEBUG_ONLY(_verifying = verifying;)
6281 }
6282
6283 void MarkFromRootsClosure::reset(HeapWord* addr) {
6284 assert(_markStack->isEmpty(), "would cause duplicates on stack");
6285 assert(_span.contains(addr), "Out of bounds _finger?");
6286 _finger = addr;
6287 _threshold = (HeapWord*)round_to(
6288 (intptr_t)_finger, CardTableModRefBS::card_size);
6289 }
6290
6291 // Should revisit to see if this should be restructured for
6292 // greater efficiency.
6293 bool MarkFromRootsClosure::do_bit(size_t offset) {
6294 if (_skipBits > 0) {
6295 _skipBits--;
6296 return true;
6297 }
6298 // convert offset into a HeapWord*
6299 HeapWord* addr = _bitMap->startWord() + offset;
6300 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
6301 "address out of range");
6302 assert(_bitMap->isMarked(addr), "tautology");
6303 if (_bitMap->isMarked(addr+1)) {
6304 // this is an allocated but not yet initialized object
6305 assert(_skipBits == 0, "tautology");
6306 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
6307 oop p = oop(addr);
6308 if (p->klass_or_null() == NULL) {
6309 DEBUG_ONLY(if (!_verifying) {)
6310 // We re-dirty the cards on which this object lies and increase
6311 // the _threshold so that we'll come back to scan this object
6312 // during the preclean or remark phase. (CMSCleanOnEnter)
6313 if (CMSCleanOnEnter) {
6314 size_t sz = _collector->block_size_using_printezis_bits(addr);
6315 HeapWord* end_card_addr = (HeapWord*)round_to(
6316 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6317 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6318 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6319 // Bump _threshold to end_card_addr; note that
6320 // _threshold cannot possibly exceed end_card_addr, anyhow.
6321 // This prevents future clearing of the card as the scan proceeds
6322 // to the right.
6323 assert(_threshold <= end_card_addr,
6324 "Because we are just scanning into this object");
6325 if (_threshold < end_card_addr) {
6326 _threshold = end_card_addr;
6327 }
6328 if (p->klass_or_null() != NULL) {
6329 // Redirty the range of cards...
6330 _mut->mark_range(redirty_range);
6331 } // ...else the setting of klass will dirty the card anyway.
6332 }
6333 DEBUG_ONLY(})
6334 return true;
6335 }
6336 }
6337 scanOopsInOop(addr);
6338 return true;
6339 }
6340
6341 // We take a break if we've been at this for a while,
6342 // so as to avoid monopolizing the locks involved.
6343 void MarkFromRootsClosure::do_yield_work() {
6344 // First give up the locks, then yield, then re-lock
6345 // We should probably use a constructor/destructor idiom to
6346 // do this unlock/lock or modify the MutexUnlocker class to
6347 // serve our purpose. XXX
6348 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6349 "CMS thread should hold CMS token");
6350 assert_lock_strong(_bitMap->lock());
6351 _bitMap->lock()->unlock();
6352 ConcurrentMarkSweepThread::desynchronize(true);
6353 _collector->stopTimer();
6354 _collector->incrementYields();
6355
6356 // See the comment in coordinator_yield()
6357 for (unsigned i = 0; i < CMSYieldSleepCount &&
6358 ConcurrentMarkSweepThread::should_yield() &&
6359 !CMSCollector::foregroundGCIsActive(); ++i) {
6360 os::sleep(Thread::current(), 1, false);
6361 }
6362
6363 ConcurrentMarkSweepThread::synchronize(true);
6364 _bitMap->lock()->lock_without_safepoint_check();
6365 _collector->startTimer();
6366 }
6367
6368 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
6369 assert(_bitMap->isMarked(ptr), "expected bit to be set");
6370 assert(_markStack->isEmpty(),
6371 "should drain stack to limit stack usage");
6372 // convert ptr to an oop preparatory to scanning
6373 oop obj = oop(ptr);
6374 // Ignore mark word in verification below, since we
6375 // may be running concurrent with mutators.
6376 assert(obj->is_oop(true), "should be an oop");
6377 assert(_finger <= ptr, "_finger runneth ahead");
6378 // advance the finger to right end of this object
6379 _finger = ptr + obj->size();
6380 assert(_finger > ptr, "we just incremented it above");
6381 // On large heaps, it may take us some time to get through
6382 // the marking phase. During
6383 // this time it's possible that a lot of mutations have
6384 // accumulated in the card table and the mod union table --
6385 // these mutation records are redundant until we have
6386 // actually traced into the corresponding card.
6387 // Here, we check whether advancing the finger would make
6388 // us cross into a new card, and if so clear corresponding
6389 // cards in the MUT (preclean them in the card-table in the
6390 // future).
6391
6392 DEBUG_ONLY(if (!_verifying) {)
6393 // The clean-on-enter optimization is disabled by default,
6394 // until we fix 6178663.
6395 if (CMSCleanOnEnter && (_finger > _threshold)) {
6396 // [_threshold, _finger) represents the interval
6397 // of cards to be cleared in MUT (or precleaned in card table).
6398 // The set of cards to be cleared is all those that overlap
6399 // with the interval [_threshold, _finger); note that
6400 // _threshold is always kept card-aligned but _finger isn't
6401 // always card-aligned.
6402 HeapWord* old_threshold = _threshold;
6403 assert(old_threshold == (HeapWord*)round_to(
6404 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6405 "_threshold should always be card-aligned");
6406 _threshold = (HeapWord*)round_to(
6407 (intptr_t)_finger, CardTableModRefBS::card_size);
6408 MemRegion mr(old_threshold, _threshold);
6409 assert(!mr.is_empty(), "Control point invariant");
6410 assert(_span.contains(mr), "Should clear within span");
6411 _mut->clear_range(mr);
6412 }
6413 DEBUG_ONLY(})
6414 // Note: the finger doesn't advance while we drain
6415 // the stack below.
6416 PushOrMarkClosure pushOrMarkClosure(_collector,
6417 _span, _bitMap, _markStack,
6418 _finger, this);
6419 bool res = _markStack->push(obj);
6420 assert(res, "Empty non-zero size stack should have space for single push");
6421 while (!_markStack->isEmpty()) {
6422 oop new_oop = _markStack->pop();
6423 // Skip verifying header mark word below because we are
6424 // running concurrent with mutators.
6425 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6426 // now scan this oop's oops
6427 new_oop->oop_iterate(&pushOrMarkClosure);
6428 do_yield_check();
6429 }
6430 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
6431 }
6432
6433 ParMarkFromRootsClosure::ParMarkFromRootsClosure(CMSConcMarkingTask* task,
6434 CMSCollector* collector, MemRegion span,
6435 CMSBitMap* bit_map,
6436 OopTaskQueue* work_queue,
6437 CMSMarkStack* overflow_stack):
6438 _collector(collector),
6439 _whole_span(collector->_span),
6440 _span(span),
6441 _bit_map(bit_map),
6442 _mut(&collector->_modUnionTable),
6443 _work_queue(work_queue),
6444 _overflow_stack(overflow_stack),
6445 _skip_bits(0),
6446 _task(task)
6447 {
6448 assert(_work_queue->size() == 0, "work_queue should be empty");
6449 _finger = span.start();
6450 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
6451 assert(_span.contains(_finger), "Out of bounds _finger?");
6452 }
6453
6454 // Should revisit to see if this should be restructured for
6455 // greater efficiency.
6456 bool ParMarkFromRootsClosure::do_bit(size_t offset) {
6457 if (_skip_bits > 0) {
6458 _skip_bits--;
6459 return true;
6460 }
6461 // convert offset into a HeapWord*
6462 HeapWord* addr = _bit_map->startWord() + offset;
6463 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
6464 "address out of range");
6465 assert(_bit_map->isMarked(addr), "tautology");
6466 if (_bit_map->isMarked(addr+1)) {
6467 // this is an allocated object that might not yet be initialized
6468 assert(_skip_bits == 0, "tautology");
6469 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
6470 oop p = oop(addr);
6471 if (p->klass_or_null() == NULL) {
6472 // in the case of Clean-on-Enter optimization, redirty card
6473 // and avoid clearing card by increasing the threshold.
6474 return true;
6475 }
6476 }
6477 scan_oops_in_oop(addr);
6478 return true;
6479 }
6480
6481 void ParMarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
6482 assert(_bit_map->isMarked(ptr), "expected bit to be set");
6483 // Should we assert that our work queue is empty or
6484 // below some drain limit?
6485 assert(_work_queue->size() == 0,
6486 "should drain stack to limit stack usage");
6487 // convert ptr to an oop preparatory to scanning
6488 oop obj = oop(ptr);
6489 // Ignore mark word in verification below, since we
6490 // may be running concurrent with mutators.
6491 assert(obj->is_oop(true), "should be an oop");
6492 assert(_finger <= ptr, "_finger runneth ahead");
6493 // advance the finger to right end of this object
6494 _finger = ptr + obj->size();
6495 assert(_finger > ptr, "we just incremented it above");
6496 // On large heaps, it may take us some time to get through
6497 // the marking phase. During
6498 // this time it's possible that a lot of mutations have
6499 // accumulated in the card table and the mod union table --
6500 // these mutation records are redundant until we have
6501 // actually traced into the corresponding card.
6502 // Here, we check whether advancing the finger would make
6503 // us cross into a new card, and if so clear corresponding
6504 // cards in the MUT (preclean them in the card-table in the
6505 // future).
6506
6507 // The clean-on-enter optimization is disabled by default,
6508 // until we fix 6178663.
6509 if (CMSCleanOnEnter && (_finger > _threshold)) {
6510 // [_threshold, _finger) represents the interval
6511 // of cards to be cleared in MUT (or precleaned in card table).
6512 // The set of cards to be cleared is all those that overlap
6513 // with the interval [_threshold, _finger); note that
6514 // _threshold is always kept card-aligned but _finger isn't
6515 // always card-aligned.
6516 HeapWord* old_threshold = _threshold;
6517 assert(old_threshold == (HeapWord*)round_to(
6518 (intptr_t)old_threshold, CardTableModRefBS::card_size),
6519 "_threshold should always be card-aligned");
6520 _threshold = (HeapWord*)round_to(
6521 (intptr_t)_finger, CardTableModRefBS::card_size);
6522 MemRegion mr(old_threshold, _threshold);
6523 assert(!mr.is_empty(), "Control point invariant");
6524 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
6525 _mut->clear_range(mr);
6526 }
6527
6528 // Note: the local finger doesn't advance while we drain
6529 // the stack below, but the global finger sure can and will.
6530 HeapWord** gfa = _task->global_finger_addr();
6531 ParPushOrMarkClosure pushOrMarkClosure(_collector,
6532 _span, _bit_map,
6533 _work_queue,
6534 _overflow_stack,
6535 _finger,
6536 gfa, this);
6537 bool res = _work_queue->push(obj); // overflow could occur here
6538 assert(res, "Will hold once we use workqueues");
6539 while (true) {
6540 oop new_oop;
6541 if (!_work_queue->pop_local(new_oop)) {
6542 // We emptied our work_queue; check if there's stuff that can
6543 // be gotten from the overflow stack.
6544 if (CMSConcMarkingTask::get_work_from_overflow_stack(
6545 _overflow_stack, _work_queue)) {
6546 do_yield_check();
6547 continue;
6548 } else { // done
6549 break;
6550 }
6551 }
6552 // Skip verifying header mark word below because we are
6553 // running concurrent with mutators.
6554 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
6555 // now scan this oop's oops
6556 new_oop->oop_iterate(&pushOrMarkClosure);
6557 do_yield_check();
6558 }
6559 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
6560 }
6561
6562 // Yield in response to a request from VM Thread or
6563 // from mutators.
6564 void ParMarkFromRootsClosure::do_yield_work() {
6565 assert(_task != NULL, "sanity");
6566 _task->yield();
6567 }
6568
6569 // A variant of the above used for verifying CMS marking work.
6570 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
6571 MemRegion span,
6572 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6573 CMSMarkStack* mark_stack):
6574 _collector(collector),
6575 _span(span),
6576 _verification_bm(verification_bm),
6577 _cms_bm(cms_bm),
6578 _mark_stack(mark_stack),
6579 _pam_verify_closure(collector, span, verification_bm, cms_bm,
6580 mark_stack)
6581 {
6582 assert(_mark_stack->isEmpty(), "stack should be empty");
6583 _finger = _verification_bm->startWord();
6584 assert(_collector->_restart_addr == NULL, "Sanity check");
6585 assert(_span.contains(_finger), "Out of bounds _finger?");
6586 }
6587
6588 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
6589 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
6590 assert(_span.contains(addr), "Out of bounds _finger?");
6591 _finger = addr;
6592 }
6593
6594 // Should revisit to see if this should be restructured for
6595 // greater efficiency.
6596 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
6597 // convert offset into a HeapWord*
6598 HeapWord* addr = _verification_bm->startWord() + offset;
6599 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
6600 "address out of range");
6601 assert(_verification_bm->isMarked(addr), "tautology");
6602 assert(_cms_bm->isMarked(addr), "tautology");
6603
6604 assert(_mark_stack->isEmpty(),
6605 "should drain stack to limit stack usage");
6606 // convert addr to an oop preparatory to scanning
6607 oop obj = oop(addr);
6608 assert(obj->is_oop(), "should be an oop");
6609 assert(_finger <= addr, "_finger runneth ahead");
6610 // advance the finger to right end of this object
6611 _finger = addr + obj->size();
6612 assert(_finger > addr, "we just incremented it above");
6613 // Note: the finger doesn't advance while we drain
6614 // the stack below.
6615 bool res = _mark_stack->push(obj);
6616 assert(res, "Empty non-zero size stack should have space for single push");
6617 while (!_mark_stack->isEmpty()) {
6618 oop new_oop = _mark_stack->pop();
6619 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
6620 // now scan this oop's oops
6621 new_oop->oop_iterate(&_pam_verify_closure);
6622 }
6623 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
6624 return true;
6625 }
6626
6627 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
6628 CMSCollector* collector, MemRegion span,
6629 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
6630 CMSMarkStack* mark_stack):
6631 MetadataAwareOopClosure(collector->ref_processor()),
6632 _collector(collector),
6633 _span(span),
6634 _verification_bm(verification_bm),
6635 _cms_bm(cms_bm),
6636 _mark_stack(mark_stack)
6637 { }
6638
6639 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6640 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
6641
6642 // Upon stack overflow, we discard (part of) the stack,
6643 // remembering the least address amongst those discarded
6644 // in CMSCollector's _restart_address.
6645 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
6646 // Remember the least grey address discarded
6647 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
6648 _collector->lower_restart_addr(ra);
6649 _mark_stack->reset(); // discard stack contents
6650 _mark_stack->expand(); // expand the stack if possible
6651 }
6652
6653 void PushAndMarkVerifyClosure::do_oop(oop obj) {
6654 assert(obj->is_oop_or_null(), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6655 HeapWord* addr = (HeapWord*)obj;
6656 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
6657 // Oop lies in _span and isn't yet grey or black
6658 _verification_bm->mark(addr); // now grey
6659 if (!_cms_bm->isMarked(addr)) {
6660 Log(gc, verify) log;
6661 ResourceMark rm;
6662 oop(addr)->print_on(log.error_stream());
6663 log.error(" (" INTPTR_FORMAT " should have been marked)", p2i(addr));
6664 fatal("... aborting");
6665 }
6666
6667 if (!_mark_stack->push(obj)) { // stack overflow
6668 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _mark_stack->capacity());
6669 assert(_mark_stack->isFull(), "Else push should have succeeded");
6670 handle_stack_overflow(addr);
6671 }
6672 // anything including and to the right of _finger
6673 // will be scanned as we iterate over the remainder of the
6674 // bit map
6675 }
6676 }
6677
6678 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
6679 MemRegion span,
6680 CMSBitMap* bitMap, CMSMarkStack* markStack,
6681 HeapWord* finger, MarkFromRootsClosure* parent) :
6682 MetadataAwareOopClosure(collector->ref_processor()),
6683 _collector(collector),
6684 _span(span),
6685 _bitMap(bitMap),
6686 _markStack(markStack),
6687 _finger(finger),
6688 _parent(parent)
6689 { }
6690
6691 ParPushOrMarkClosure::ParPushOrMarkClosure(CMSCollector* collector,
6692 MemRegion span,
6693 CMSBitMap* bit_map,
6694 OopTaskQueue* work_queue,
6695 CMSMarkStack* overflow_stack,
6696 HeapWord* finger,
6697 HeapWord** global_finger_addr,
6698 ParMarkFromRootsClosure* parent) :
6699 MetadataAwareOopClosure(collector->ref_processor()),
6700 _collector(collector),
6701 _whole_span(collector->_span),
6702 _span(span),
6703 _bit_map(bit_map),
6704 _work_queue(work_queue),
6705 _overflow_stack(overflow_stack),
6706 _finger(finger),
6707 _global_finger_addr(global_finger_addr),
6708 _parent(parent)
6709 { }
6710
6711 // Assumes thread-safe access by callers, who are
6712 // responsible for mutual exclusion.
6713 void CMSCollector::lower_restart_addr(HeapWord* low) {
6714 assert(_span.contains(low), "Out of bounds addr");
6715 if (_restart_addr == NULL) {
6716 _restart_addr = low;
6717 } else {
6718 _restart_addr = MIN2(_restart_addr, low);
6719 }
6720 }
6721
6722 // Upon stack overflow, we discard (part of) the stack,
6723 // remembering the least address amongst those discarded
6724 // in CMSCollector's _restart_address.
6725 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6726 // Remember the least grey address discarded
6727 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
6728 _collector->lower_restart_addr(ra);
6729 _markStack->reset(); // discard stack contents
6730 _markStack->expand(); // expand the stack if possible
6731 }
6732
6733 // Upon stack overflow, we discard (part of) the stack,
6734 // remembering the least address amongst those discarded
6735 // in CMSCollector's _restart_address.
6736 void ParPushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
6737 // We need to do this under a mutex to prevent other
6738 // workers from interfering with the work done below.
6739 MutexLockerEx ml(_overflow_stack->par_lock(),
6740 Mutex::_no_safepoint_check_flag);
6741 // Remember the least grey address discarded
6742 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
6743 _collector->lower_restart_addr(ra);
6744 _overflow_stack->reset(); // discard stack contents
6745 _overflow_stack->expand(); // expand the stack if possible
6746 }
6747
6748 void PushOrMarkClosure::do_oop(oop obj) {
6749 // Ignore mark word because we are running concurrent with mutators.
6750 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6751 HeapWord* addr = (HeapWord*)obj;
6752 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
6753 // Oop lies in _span and isn't yet grey or black
6754 _bitMap->mark(addr); // now grey
6755 if (addr < _finger) {
6756 // the bit map iteration has already either passed, or
6757 // sampled, this bit in the bit map; we'll need to
6758 // use the marking stack to scan this oop's oops.
6759 bool simulate_overflow = false;
6760 NOT_PRODUCT(
6761 if (CMSMarkStackOverflowALot &&
6762 _collector->simulate_overflow()) {
6763 // simulate a stack overflow
6764 simulate_overflow = true;
6765 }
6766 )
6767 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
6768 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _markStack->capacity());
6769 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
6770 handle_stack_overflow(addr);
6771 }
6772 }
6773 // anything including and to the right of _finger
6774 // will be scanned as we iterate over the remainder of the
6775 // bit map
6776 do_yield_check();
6777 }
6778 }
6779
6780 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
6781 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
6782
6783 void ParPushOrMarkClosure::do_oop(oop obj) {
6784 // Ignore mark word because we are running concurrent with mutators.
6785 assert(obj->is_oop_or_null(true), "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6786 HeapWord* addr = (HeapWord*)obj;
6787 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
6788 // Oop lies in _span and isn't yet grey or black
6789 // We read the global_finger (volatile read) strictly after marking oop
6790 bool res = _bit_map->par_mark(addr); // now grey
6791 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
6792 // Should we push this marked oop on our stack?
6793 // -- if someone else marked it, nothing to do
6794 // -- if target oop is above global finger nothing to do
6795 // -- if target oop is in chunk and above local finger
6796 // then nothing to do
6797 // -- else push on work queue
6798 if ( !res // someone else marked it, they will deal with it
6799 || (addr >= *gfa) // will be scanned in a later task
6800 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
6801 return;
6802 }
6803 // the bit map iteration has already either passed, or
6804 // sampled, this bit in the bit map; we'll need to
6805 // use the marking stack to scan this oop's oops.
6806 bool simulate_overflow = false;
6807 NOT_PRODUCT(
6808 if (CMSMarkStackOverflowALot &&
6809 _collector->simulate_overflow()) {
6810 // simulate a stack overflow
6811 simulate_overflow = true;
6812 }
6813 )
6814 if (simulate_overflow ||
6815 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
6816 // stack overflow
6817 log_trace(gc)("CMS marking stack overflow (benign) at " SIZE_FORMAT, _overflow_stack->capacity());
6818 // We cannot assert that the overflow stack is full because
6819 // it may have been emptied since.
6820 assert(simulate_overflow ||
6821 _work_queue->size() == _work_queue->max_elems(),
6822 "Else push should have succeeded");
6823 handle_stack_overflow(addr);
6824 }
6825 do_yield_check();
6826 }
6827 }
6828
6829 void ParPushOrMarkClosure::do_oop(oop* p) { ParPushOrMarkClosure::do_oop_work(p); }
6830 void ParPushOrMarkClosure::do_oop(narrowOop* p) { ParPushOrMarkClosure::do_oop_work(p); }
6831
6832 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
6833 MemRegion span,
6834 ReferenceProcessor* rp,
6835 CMSBitMap* bit_map,
6836 CMSBitMap* mod_union_table,
6837 CMSMarkStack* mark_stack,
6838 bool concurrent_precleaning):
6839 MetadataAwareOopClosure(rp),
6840 _collector(collector),
6841 _span(span),
6842 _bit_map(bit_map),
6843 _mod_union_table(mod_union_table),
6844 _mark_stack(mark_stack),
6845 _concurrent_precleaning(concurrent_precleaning)
6846 {
6847 assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6848 }
6849
6850 // Grey object rescan during pre-cleaning and second checkpoint phases --
6851 // the non-parallel version (the parallel version appears further below.)
6852 void PushAndMarkClosure::do_oop(oop obj) {
6853 // Ignore mark word verification. If during concurrent precleaning,
6854 // the object monitor may be locked. If during the checkpoint
6855 // phases, the object may already have been reached by a different
6856 // path and may be at the end of the global overflow list (so
6857 // the mark word may be NULL).
6858 assert(obj->is_oop_or_null(true /* ignore mark word */),
6859 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6860 HeapWord* addr = (HeapWord*)obj;
6861 // Check if oop points into the CMS generation
6862 // and is not marked
6863 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6864 // a white object ...
6865 _bit_map->mark(addr); // ... now grey
6866 // push on the marking stack (grey set)
6867 bool simulate_overflow = false;
6868 NOT_PRODUCT(
6869 if (CMSMarkStackOverflowALot &&
6870 _collector->simulate_overflow()) {
6871 // simulate a stack overflow
6872 simulate_overflow = true;
6873 }
6874 )
6875 if (simulate_overflow || !_mark_stack->push(obj)) {
6876 if (_concurrent_precleaning) {
6877 // During precleaning we can just dirty the appropriate card(s)
6878 // in the mod union table, thus ensuring that the object remains
6879 // in the grey set and continue. In the case of object arrays
6880 // we need to dirty all of the cards that the object spans,
6881 // since the rescan of object arrays will be limited to the
6882 // dirty cards.
6883 // Note that no one can be interfering with us in this action
6884 // of dirtying the mod union table, so no locking or atomics
6885 // are required.
6886 if (obj->is_objArray()) {
6887 size_t sz = obj->size();
6888 HeapWord* end_card_addr = (HeapWord*)round_to(
6889 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
6890 MemRegion redirty_range = MemRegion(addr, end_card_addr);
6891 assert(!redirty_range.is_empty(), "Arithmetical tautology");
6892 _mod_union_table->mark_range(redirty_range);
6893 } else {
6894 _mod_union_table->mark(addr);
6895 }
6896 _collector->_ser_pmc_preclean_ovflw++;
6897 } else {
6898 // During the remark phase, we need to remember this oop
6899 // in the overflow list.
6900 _collector->push_on_overflow_list(obj);
6901 _collector->_ser_pmc_remark_ovflw++;
6902 }
6903 }
6904 }
6905 }
6906
6907 ParPushAndMarkClosure::ParPushAndMarkClosure(CMSCollector* collector,
6908 MemRegion span,
6909 ReferenceProcessor* rp,
6910 CMSBitMap* bit_map,
6911 OopTaskQueue* work_queue):
6912 MetadataAwareOopClosure(rp),
6913 _collector(collector),
6914 _span(span),
6915 _bit_map(bit_map),
6916 _work_queue(work_queue)
6917 {
6918 assert(ref_processor() != NULL, "ref_processor shouldn't be NULL");
6919 }
6920
6921 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
6922 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
6923
6924 // Grey object rescan during second checkpoint phase --
6925 // the parallel version.
6926 void ParPushAndMarkClosure::do_oop(oop obj) {
6927 // In the assert below, we ignore the mark word because
6928 // this oop may point to an already visited object that is
6929 // on the overflow stack (in which case the mark word has
6930 // been hijacked for chaining into the overflow stack --
6931 // if this is the last object in the overflow stack then
6932 // its mark word will be NULL). Because this object may
6933 // have been subsequently popped off the global overflow
6934 // stack, and the mark word possibly restored to the prototypical
6935 // value, by the time we get to examined this failing assert in
6936 // the debugger, is_oop_or_null(false) may subsequently start
6937 // to hold.
6938 assert(obj->is_oop_or_null(true),
6939 "Expected an oop or NULL at " PTR_FORMAT, p2i(obj));
6940 HeapWord* addr = (HeapWord*)obj;
6941 // Check if oop points into the CMS generation
6942 // and is not marked
6943 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
6944 // a white object ...
6945 // If we manage to "claim" the object, by being the
6946 // first thread to mark it, then we push it on our
6947 // marking stack
6948 if (_bit_map->par_mark(addr)) { // ... now grey
6949 // push on work queue (grey set)
6950 bool simulate_overflow = false;
6951 NOT_PRODUCT(
6952 if (CMSMarkStackOverflowALot &&
6953 _collector->par_simulate_overflow()) {
6954 // simulate a stack overflow
6955 simulate_overflow = true;
6956 }
6957 )
6958 if (simulate_overflow || !_work_queue->push(obj)) {
6959 _collector->par_push_on_overflow_list(obj);
6960 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
6961 }
6962 } // Else, some other thread got there first
6963 }
6964 }
6965
6966 void ParPushAndMarkClosure::do_oop(oop* p) { ParPushAndMarkClosure::do_oop_work(p); }
6967 void ParPushAndMarkClosure::do_oop(narrowOop* p) { ParPushAndMarkClosure::do_oop_work(p); }
6968
6969 void CMSPrecleanRefsYieldClosure::do_yield_work() {
6970 Mutex* bml = _collector->bitMapLock();
6971 assert_lock_strong(bml);
6972 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6973 "CMS thread should hold CMS token");
6974
6975 bml->unlock();
6976 ConcurrentMarkSweepThread::desynchronize(true);
6977
6978 _collector->stopTimer();
6979 _collector->incrementYields();
6980
6981 // See the comment in coordinator_yield()
6982 for (unsigned i = 0; i < CMSYieldSleepCount &&
6983 ConcurrentMarkSweepThread::should_yield() &&
6984 !CMSCollector::foregroundGCIsActive(); ++i) {
6985 os::sleep(Thread::current(), 1, false);
6986 }
6987
6988 ConcurrentMarkSweepThread::synchronize(true);
6989 bml->lock();
6990
6991 _collector->startTimer();
6992 }
6993
6994 bool CMSPrecleanRefsYieldClosure::should_return() {
6995 if (ConcurrentMarkSweepThread::should_yield()) {
6996 do_yield_work();
6997 }
6998 return _collector->foregroundGCIsActive();
6999 }
7000
7001 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7002 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7003 "mr should be aligned to start at a card boundary");
7004 // We'd like to assert:
7005 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7006 // "mr should be a range of cards");
7007 // However, that would be too strong in one case -- the last
7008 // partition ends at _unallocated_block which, in general, can be
7009 // an arbitrary boundary, not necessarily card aligned.
7010 _num_dirty_cards += mr.word_size()/CardTableModRefBS::card_size_in_words;
7011 _space->object_iterate_mem(mr, &_scan_cl);
7012 }
7013
7014 SweepClosure::SweepClosure(CMSCollector* collector,
7015 ConcurrentMarkSweepGeneration* g,
7016 CMSBitMap* bitMap, bool should_yield) :
7017 _collector(collector),
7018 _g(g),
7019 _sp(g->cmsSpace()),
7020 _limit(_sp->sweep_limit()),
7021 _freelistLock(_sp->freelistLock()),
7022 _bitMap(bitMap),
7023 _yield(should_yield),
7024 _inFreeRange(false), // No free range at beginning of sweep
7025 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7026 _lastFreeRangeCoalesced(false),
7027 _freeFinger(g->used_region().start())
7028 {
7029 NOT_PRODUCT(
7030 _numObjectsFreed = 0;
7031 _numWordsFreed = 0;
7032 _numObjectsLive = 0;
7033 _numWordsLive = 0;
7034 _numObjectsAlreadyFree = 0;
7035 _numWordsAlreadyFree = 0;
7036 _last_fc = NULL;
7037
7038 _sp->initializeIndexedFreeListArrayReturnedBytes();
7039 _sp->dictionary()->initialize_dict_returned_bytes();
7040 )
7041 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7042 "sweep _limit out of bounds");
7043 log_develop_trace(gc, sweep)("====================");
7044 log_develop_trace(gc, sweep)("Starting new sweep with limit " PTR_FORMAT, p2i(_limit));
7045 }
7046
7047 void SweepClosure::print_on(outputStream* st) const {
7048 st->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7049 p2i(_sp->bottom()), p2i(_sp->end()));
7050 st->print_cr("_limit = " PTR_FORMAT, p2i(_limit));
7051 st->print_cr("_freeFinger = " PTR_FORMAT, p2i(_freeFinger));
7052 NOT_PRODUCT(st->print_cr("_last_fc = " PTR_FORMAT, p2i(_last_fc));)
7053 st->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7054 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7055 }
7056
7057 #ifndef PRODUCT
7058 // Assertion checking only: no useful work in product mode --
7059 // however, if any of the flags below become product flags,
7060 // you may need to review this code to see if it needs to be
7061 // enabled in product mode.
7062 SweepClosure::~SweepClosure() {
7063 assert_lock_strong(_freelistLock);
7064 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7065 "sweep _limit out of bounds");
7066 if (inFreeRange()) {
7067 Log(gc, sweep) log;
7068 log.error("inFreeRange() should have been reset; dumping state of SweepClosure");
7069 ResourceMark rm;
7070 print_on(log.error_stream());
7071 ShouldNotReachHere();
7072 }
7073
7074 if (log_is_enabled(Debug, gc, sweep)) {
7075 log_debug(gc, sweep)("Collected " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7076 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7077 log_debug(gc, sweep)("Live " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes Already free " SIZE_FORMAT " objects, " SIZE_FORMAT " bytes",
7078 _numObjectsLive, _numWordsLive*sizeof(HeapWord), _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7079 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * sizeof(HeapWord);
7080 log_debug(gc, sweep)("Total sweep: " SIZE_FORMAT " bytes", totalBytes);
7081 }
7082
7083 if (log_is_enabled(Trace, gc, sweep) && CMSVerifyReturnedBytes) {
7084 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7085 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7086 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7087 log_trace(gc, sweep)("Returned " SIZE_FORMAT " bytes Indexed List Returned " SIZE_FORMAT " bytes Dictionary Returned " SIZE_FORMAT " bytes",
7088 returned_bytes, indexListReturnedBytes, dict_returned_bytes);
7089 }
7090 log_develop_trace(gc, sweep)("end of sweep with _limit = " PTR_FORMAT, p2i(_limit));
7091 log_develop_trace(gc, sweep)("================");
7092 }
7093 #endif // PRODUCT
7094
7095 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7096 bool freeRangeInFreeLists) {
7097 log_develop_trace(gc, sweep)("---- Start free range at " PTR_FORMAT " with free block (%d)",
7098 p2i(freeFinger), freeRangeInFreeLists);
7099 assert(!inFreeRange(), "Trampling existing free range");
7100 set_inFreeRange(true);
7101 set_lastFreeRangeCoalesced(false);
7102
7103 set_freeFinger(freeFinger);
7104 set_freeRangeInFreeLists(freeRangeInFreeLists);
7105 if (CMSTestInFreeList) {
7106 if (freeRangeInFreeLists) {
7107 FreeChunk* fc = (FreeChunk*) freeFinger;
7108 assert(fc->is_free(), "A chunk on the free list should be free.");
7109 assert(fc->size() > 0, "Free range should have a size");
7110 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7111 }
7112 }
7113 }
7114
7115 // Note that the sweeper runs concurrently with mutators. Thus,
7116 // it is possible for direct allocation in this generation to happen
7117 // in the middle of the sweep. Note that the sweeper also coalesces
7118 // contiguous free blocks. Thus, unless the sweeper and the allocator
7119 // synchronize appropriately freshly allocated blocks may get swept up.
7120 // This is accomplished by the sweeper locking the free lists while
7121 // it is sweeping. Thus blocks that are determined to be free are
7122 // indeed free. There is however one additional complication:
7123 // blocks that have been allocated since the final checkpoint and
7124 // mark, will not have been marked and so would be treated as
7125 // unreachable and swept up. To prevent this, the allocator marks
7126 // the bit map when allocating during the sweep phase. This leads,
7127 // however, to a further complication -- objects may have been allocated
7128 // but not yet initialized -- in the sense that the header isn't yet
7129 // installed. The sweeper can not then determine the size of the block
7130 // in order to skip over it. To deal with this case, we use a technique
7131 // (due to Printezis) to encode such uninitialized block sizes in the
7132 // bit map. Since the bit map uses a bit per every HeapWord, but the
7133 // CMS generation has a minimum object size of 3 HeapWords, it follows
7134 // that "normal marks" won't be adjacent in the bit map (there will
7135 // always be at least two 0 bits between successive 1 bits). We make use
7136 // of these "unused" bits to represent uninitialized blocks -- the bit
7137 // corresponding to the start of the uninitialized object and the next
7138 // bit are both set. Finally, a 1 bit marks the end of the object that
7139 // started with the two consecutive 1 bits to indicate its potentially
7140 // uninitialized state.
7141
7142 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7143 FreeChunk* fc = (FreeChunk*)addr;
7144 size_t res;
7145
7146 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7147 // than "addr == _limit" because although _limit was a block boundary when
7148 // we started the sweep, it may no longer be one because heap expansion
7149 // may have caused us to coalesce the block ending at the address _limit
7150 // with a newly expanded chunk (this happens when _limit was set to the
7151 // previous _end of the space), so we may have stepped past _limit:
7152 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7153 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7154 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7155 "sweep _limit out of bounds");
7156 assert(addr < _sp->end(), "addr out of bounds");
7157 // Flush any free range we might be holding as a single
7158 // coalesced chunk to the appropriate free list.
7159 if (inFreeRange()) {
7160 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
7161 "freeFinger() " PTR_FORMAT " is out-of-bounds", p2i(freeFinger()));
7162 flush_cur_free_chunk(freeFinger(),
7163 pointer_delta(addr, freeFinger()));
7164 log_develop_trace(gc, sweep)("Sweep: last chunk: put_free_blk " PTR_FORMAT " (" SIZE_FORMAT ") [coalesced:%d]",
7165 p2i(freeFinger()), pointer_delta(addr, freeFinger()),
7166 lastFreeRangeCoalesced() ? 1 : 0);
7167 }
7168
7169 // help the iterator loop finish
7170 return pointer_delta(_sp->end(), addr);
7171 }
7172
7173 assert(addr < _limit, "sweep invariant");
7174 // check if we should yield
7175 do_yield_check(addr);
7176 if (fc->is_free()) {
7177 // Chunk that is already free
7178 res = fc->size();
7179 do_already_free_chunk(fc);
7180 debug_only(_sp->verifyFreeLists());
7181 // If we flush the chunk at hand in lookahead_and_flush()
7182 // and it's coalesced with a preceding chunk, then the
7183 // process of "mangling" the payload of the coalesced block
7184 // will cause erasure of the size information from the
7185 // (erstwhile) header of all the coalesced blocks but the
7186 // first, so the first disjunct in the assert will not hold
7187 // in that specific case (in which case the second disjunct
7188 // will hold).
7189 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
7190 "Otherwise the size info doesn't change at this step");
7191 NOT_PRODUCT(
7192 _numObjectsAlreadyFree++;
7193 _numWordsAlreadyFree += res;
7194 )
7195 NOT_PRODUCT(_last_fc = fc;)
7196 } else if (!_bitMap->isMarked(addr)) {
7197 // Chunk is fresh garbage
7198 res = do_garbage_chunk(fc);
7199 debug_only(_sp->verifyFreeLists());
7200 NOT_PRODUCT(
7201 _numObjectsFreed++;
7202 _numWordsFreed += res;
7203 )
7204 } else {
7205 // Chunk that is alive.
7206 res = do_live_chunk(fc);
7207 debug_only(_sp->verifyFreeLists());
7208 NOT_PRODUCT(
7209 _numObjectsLive++;
7210 _numWordsLive += res;
7211 )
7212 }
7213 return res;
7214 }
7215
7216 // For the smart allocation, record following
7217 // split deaths - a free chunk is removed from its free list because
7218 // it is being split into two or more chunks.
7219 // split birth - a free chunk is being added to its free list because
7220 // a larger free chunk has been split and resulted in this free chunk.
7221 // coal death - a free chunk is being removed from its free list because
7222 // it is being coalesced into a large free chunk.
7223 // coal birth - a free chunk is being added to its free list because
7224 // it was created when two or more free chunks where coalesced into
7225 // this free chunk.
7226 //
7227 // These statistics are used to determine the desired number of free
7228 // chunks of a given size. The desired number is chosen to be relative
7229 // to the end of a CMS sweep. The desired number at the end of a sweep
7230 // is the
7231 // count-at-end-of-previous-sweep (an amount that was enough)
7232 // - count-at-beginning-of-current-sweep (the excess)
7233 // + split-births (gains in this size during interval)
7234 // - split-deaths (demands on this size during interval)
7235 // where the interval is from the end of one sweep to the end of the
7236 // next.
7237 //
7238 // When sweeping the sweeper maintains an accumulated chunk which is
7239 // the chunk that is made up of chunks that have been coalesced. That
7240 // will be termed the left-hand chunk. A new chunk of garbage that
7241 // is being considered for coalescing will be referred to as the
7242 // right-hand chunk.
7243 //
7244 // When making a decision on whether to coalesce a right-hand chunk with
7245 // the current left-hand chunk, the current count vs. the desired count
7246 // of the left-hand chunk is considered. Also if the right-hand chunk
7247 // is near the large chunk at the end of the heap (see
7248 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
7249 // left-hand chunk is coalesced.
7250 //
7251 // When making a decision about whether to split a chunk, the desired count
7252 // vs. the current count of the candidate to be split is also considered.
7253 // If the candidate is underpopulated (currently fewer chunks than desired)
7254 // a chunk of an overpopulated (currently more chunks than desired) size may
7255 // be chosen. The "hint" associated with a free list, if non-null, points
7256 // to a free list which may be overpopulated.
7257 //
7258
7259 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
7260 const size_t size = fc->size();
7261 // Chunks that cannot be coalesced are not in the
7262 // free lists.
7263 if (CMSTestInFreeList && !fc->cantCoalesce()) {
7264 assert(_sp->verify_chunk_in_free_list(fc),
7265 "free chunk should be in free lists");
7266 }
7267 // a chunk that is already free, should not have been
7268 // marked in the bit map
7269 HeapWord* const addr = (HeapWord*) fc;
7270 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
7271 // Verify that the bit map has no bits marked between
7272 // addr and purported end of this block.
7273 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7274
7275 // Some chunks cannot be coalesced under any circumstances.
7276 // See the definition of cantCoalesce().
7277 if (!fc->cantCoalesce()) {
7278 // This chunk can potentially be coalesced.
7279 // All the work is done in
7280 do_post_free_or_garbage_chunk(fc, size);
7281 // Note that if the chunk is not coalescable (the else arm
7282 // below), we unconditionally flush, without needing to do
7283 // a "lookahead," as we do below.
7284 if (inFreeRange()) lookahead_and_flush(fc, size);
7285 } else {
7286 // Code path common to both original and adaptive free lists.
7287
7288 // cant coalesce with previous block; this should be treated
7289 // as the end of a free run if any
7290 if (inFreeRange()) {
7291 // we kicked some butt; time to pick up the garbage
7292 assert(freeFinger() < addr, "freeFinger points too high");
7293 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7294 }
7295 // else, nothing to do, just continue
7296 }
7297 }
7298
7299 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
7300 // This is a chunk of garbage. It is not in any free list.
7301 // Add it to a free list or let it possibly be coalesced into
7302 // a larger chunk.
7303 HeapWord* const addr = (HeapWord*) fc;
7304 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7305
7306 // Verify that the bit map has no bits marked between
7307 // addr and purported end of just dead object.
7308 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
7309 do_post_free_or_garbage_chunk(fc, size);
7310
7311 assert(_limit >= addr + size,
7312 "A freshly garbage chunk can't possibly straddle over _limit");
7313 if (inFreeRange()) lookahead_and_flush(fc, size);
7314 return size;
7315 }
7316
7317 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
7318 HeapWord* addr = (HeapWord*) fc;
7319 // The sweeper has just found a live object. Return any accumulated
7320 // left hand chunk to the free lists.
7321 if (inFreeRange()) {
7322 assert(freeFinger() < addr, "freeFinger points too high");
7323 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7324 }
7325
7326 // This object is live: we'd normally expect this to be
7327 // an oop, and like to assert the following:
7328 // assert(oop(addr)->is_oop(), "live block should be an oop");
7329 // However, as we commented above, this may be an object whose
7330 // header hasn't yet been initialized.
7331 size_t size;
7332 assert(_bitMap->isMarked(addr), "Tautology for this control point");
7333 if (_bitMap->isMarked(addr + 1)) {
7334 // Determine the size from the bit map, rather than trying to
7335 // compute it from the object header.
7336 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
7337 size = pointer_delta(nextOneAddr + 1, addr);
7338 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
7339 "alignment problem");
7340
7341 #ifdef ASSERT
7342 if (oop(addr)->klass_or_null() != NULL) {
7343 // Ignore mark word because we are running concurrent with mutators
7344 assert(oop(addr)->is_oop(true), "live block should be an oop");
7345 assert(size ==
7346 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
7347 "P-mark and computed size do not agree");
7348 }
7349 #endif
7350
7351 } else {
7352 // This should be an initialized object that's alive.
7353 assert(oop(addr)->klass_or_null() != NULL,
7354 "Should be an initialized object");
7355 // Ignore mark word because we are running concurrent with mutators
7356 assert(oop(addr)->is_oop(true), "live block should be an oop");
7357 // Verify that the bit map has no bits marked between
7358 // addr and purported end of this block.
7359 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
7360 assert(size >= 3, "Necessary for Printezis marks to work");
7361 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
7362 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
7363 }
7364 return size;
7365 }
7366
7367 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
7368 size_t chunkSize) {
7369 // do_post_free_or_garbage_chunk() should only be called in the case
7370 // of the adaptive free list allocator.
7371 const bool fcInFreeLists = fc->is_free();
7372 assert((HeapWord*)fc <= _limit, "sweep invariant");
7373 if (CMSTestInFreeList && fcInFreeLists) {
7374 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
7375 }
7376
7377 log_develop_trace(gc, sweep)(" -- pick up another chunk at " PTR_FORMAT " (" SIZE_FORMAT ")", p2i(fc), chunkSize);
7378
7379 HeapWord* const fc_addr = (HeapWord*) fc;
7380
7381 bool coalesce = false;
7382 const size_t left = pointer_delta(fc_addr, freeFinger());
7383 const size_t right = chunkSize;
7384 switch (FLSCoalescePolicy) {
7385 // numeric value forms a coalition aggressiveness metric
7386 case 0: { // never coalesce
7387 coalesce = false;
7388 break;
7389 }
7390 case 1: { // coalesce if left & right chunks on overpopulated lists
7391 coalesce = _sp->coalOverPopulated(left) &&
7392 _sp->coalOverPopulated(right);
7393 break;
7394 }
7395 case 2: { // coalesce if left chunk on overpopulated list (default)
7396 coalesce = _sp->coalOverPopulated(left);
7397 break;
7398 }
7399 case 3: { // coalesce if left OR right chunk on overpopulated list
7400 coalesce = _sp->coalOverPopulated(left) ||
7401 _sp->coalOverPopulated(right);
7402 break;
7403 }
7404 case 4: { // always coalesce
7405 coalesce = true;
7406 break;
7407 }
7408 default:
7409 ShouldNotReachHere();
7410 }
7411
7412 // Should the current free range be coalesced?
7413 // If the chunk is in a free range and either we decided to coalesce above
7414 // or the chunk is near the large block at the end of the heap
7415 // (isNearLargestChunk() returns true), then coalesce this chunk.
7416 const bool doCoalesce = inFreeRange()
7417 && (coalesce || _g->isNearLargestChunk(fc_addr));
7418 if (doCoalesce) {
7419 // Coalesce the current free range on the left with the new
7420 // chunk on the right. If either is on a free list,
7421 // it must be removed from the list and stashed in the closure.
7422 if (freeRangeInFreeLists()) {
7423 FreeChunk* const ffc = (FreeChunk*)freeFinger();
7424 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
7425 "Size of free range is inconsistent with chunk size.");
7426 if (CMSTestInFreeList) {
7427 assert(_sp->verify_chunk_in_free_list(ffc),
7428 "Chunk is not in free lists");
7429 }
7430 _sp->coalDeath(ffc->size());
7431 _sp->removeFreeChunkFromFreeLists(ffc);
7432 set_freeRangeInFreeLists(false);
7433 }
7434 if (fcInFreeLists) {
7435 _sp->coalDeath(chunkSize);
7436 assert(fc->size() == chunkSize,
7437 "The chunk has the wrong size or is not in the free lists");
7438 _sp->removeFreeChunkFromFreeLists(fc);
7439 }
7440 set_lastFreeRangeCoalesced(true);
7441 print_free_block_coalesced(fc);
7442 } else { // not in a free range and/or should not coalesce
7443 // Return the current free range and start a new one.
7444 if (inFreeRange()) {
7445 // In a free range but cannot coalesce with the right hand chunk.
7446 // Put the current free range into the free lists.
7447 flush_cur_free_chunk(freeFinger(),
7448 pointer_delta(fc_addr, freeFinger()));
7449 }
7450 // Set up for new free range. Pass along whether the right hand
7451 // chunk is in the free lists.
7452 initialize_free_range((HeapWord*)fc, fcInFreeLists);
7453 }
7454 }
7455
7456 // Lookahead flush:
7457 // If we are tracking a free range, and this is the last chunk that
7458 // we'll look at because its end crosses past _limit, we'll preemptively
7459 // flush it along with any free range we may be holding on to. Note that
7460 // this can be the case only for an already free or freshly garbage
7461 // chunk. If this block is an object, it can never straddle
7462 // over _limit. The "straddling" occurs when _limit is set at
7463 // the previous end of the space when this cycle started, and
7464 // a subsequent heap expansion caused the previously co-terminal
7465 // free block to be coalesced with the newly expanded portion,
7466 // thus rendering _limit a non-block-boundary making it dangerous
7467 // for the sweeper to step over and examine.
7468 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
7469 assert(inFreeRange(), "Should only be called if currently in a free range.");
7470 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
7471 assert(_sp->used_region().contains(eob - 1),
7472 "eob = " PTR_FORMAT " eob-1 = " PTR_FORMAT " _limit = " PTR_FORMAT
7473 " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
7474 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
7475 p2i(eob), p2i(eob-1), p2i(_limit), p2i(_sp->bottom()), p2i(_sp->end()), p2i(fc), chunk_size);
7476 if (eob >= _limit) {
7477 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
7478 log_develop_trace(gc, sweep)("_limit " PTR_FORMAT " reached or crossed by block "
7479 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
7480 "[" PTR_FORMAT "," PTR_FORMAT ")",
7481 p2i(_limit), p2i(fc), p2i(eob), p2i(_sp->bottom()), p2i(_sp->end()));
7482 // Return the storage we are tracking back into the free lists.
7483 log_develop_trace(gc, sweep)("Flushing ... ");
7484 assert(freeFinger() < eob, "Error");
7485 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
7486 }
7487 }
7488
7489 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
7490 assert(inFreeRange(), "Should only be called if currently in a free range.");
7491 assert(size > 0,
7492 "A zero sized chunk cannot be added to the free lists.");
7493 if (!freeRangeInFreeLists()) {
7494 if (CMSTestInFreeList) {
7495 FreeChunk* fc = (FreeChunk*) chunk;
7496 fc->set_size(size);
7497 assert(!_sp->verify_chunk_in_free_list(fc),
7498 "chunk should not be in free lists yet");
7499 }
7500 log_develop_trace(gc, sweep)(" -- add free block " PTR_FORMAT " (" SIZE_FORMAT ") to free lists", p2i(chunk), size);
7501 // A new free range is going to be starting. The current
7502 // free range has not been added to the free lists yet or
7503 // was removed so add it back.
7504 // If the current free range was coalesced, then the death
7505 // of the free range was recorded. Record a birth now.
7506 if (lastFreeRangeCoalesced()) {
7507 _sp->coalBirth(size);
7508 }
7509 _sp->addChunkAndRepairOffsetTable(chunk, size,
7510 lastFreeRangeCoalesced());
7511 } else {
7512 log_develop_trace(gc, sweep)("Already in free list: nothing to flush");
7513 }
7514 set_inFreeRange(false);
7515 set_freeRangeInFreeLists(false);
7516 }
7517
7518 // We take a break if we've been at this for a while,
7519 // so as to avoid monopolizing the locks involved.
7520 void SweepClosure::do_yield_work(HeapWord* addr) {
7521 // Return current free chunk being used for coalescing (if any)
7522 // to the appropriate freelist. After yielding, the next
7523 // free block encountered will start a coalescing range of
7524 // free blocks. If the next free block is adjacent to the
7525 // chunk just flushed, they will need to wait for the next
7526 // sweep to be coalesced.
7527 if (inFreeRange()) {
7528 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
7529 }
7530
7531 // First give up the locks, then yield, then re-lock.
7532 // We should probably use a constructor/destructor idiom to
7533 // do this unlock/lock or modify the MutexUnlocker class to
7534 // serve our purpose. XXX
7535 assert_lock_strong(_bitMap->lock());
7536 assert_lock_strong(_freelistLock);
7537 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7538 "CMS thread should hold CMS token");
7539 _bitMap->lock()->unlock();
7540 _freelistLock->unlock();
7541 ConcurrentMarkSweepThread::desynchronize(true);
7542 _collector->stopTimer();
7543 _collector->incrementYields();
7544
7545 // See the comment in coordinator_yield()
7546 for (unsigned i = 0; i < CMSYieldSleepCount &&
7547 ConcurrentMarkSweepThread::should_yield() &&
7548 !CMSCollector::foregroundGCIsActive(); ++i) {
7549 os::sleep(Thread::current(), 1, false);
7550 }
7551
7552 ConcurrentMarkSweepThread::synchronize(true);
7553 _freelistLock->lock();
7554 _bitMap->lock()->lock_without_safepoint_check();
7555 _collector->startTimer();
7556 }
7557
7558 #ifndef PRODUCT
7559 // This is actually very useful in a product build if it can
7560 // be called from the debugger. Compile it into the product
7561 // as needed.
7562 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
7563 return debug_cms_space->verify_chunk_in_free_list(fc);
7564 }
7565 #endif
7566
7567 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
7568 log_develop_trace(gc, sweep)("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
7569 p2i(fc), fc->size());
7570 }
7571
7572 // CMSIsAliveClosure
7573 bool CMSIsAliveClosure::do_object_b(oop obj) {
7574 HeapWord* addr = (HeapWord*)obj;
7575 return addr != NULL &&
7576 (!_span.contains(addr) || _bit_map->isMarked(addr));
7577 }
7578
7579
7580 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
7581 MemRegion span,
7582 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
7583 bool cpc):
7584 _collector(collector),
7585 _span(span),
7586 _bit_map(bit_map),
7587 _mark_stack(mark_stack),
7588 _concurrent_precleaning(cpc) {
7589 assert(!_span.is_empty(), "Empty span could spell trouble");
7590 }
7591
7592
7593 // CMSKeepAliveClosure: the serial version
7594 void CMSKeepAliveClosure::do_oop(oop obj) {
7595 HeapWord* addr = (HeapWord*)obj;
7596 if (_span.contains(addr) &&
7597 !_bit_map->isMarked(addr)) {
7598 _bit_map->mark(addr);
7599 bool simulate_overflow = false;
7600 NOT_PRODUCT(
7601 if (CMSMarkStackOverflowALot &&
7602 _collector->simulate_overflow()) {
7603 // simulate a stack overflow
7604 simulate_overflow = true;
7605 }
7606 )
7607 if (simulate_overflow || !_mark_stack->push(obj)) {
7608 if (_concurrent_precleaning) {
7609 // We dirty the overflown object and let the remark
7610 // phase deal with it.
7611 assert(_collector->overflow_list_is_empty(), "Error");
7612 // In the case of object arrays, we need to dirty all of
7613 // the cards that the object spans. No locking or atomics
7614 // are needed since no one else can be mutating the mod union
7615 // table.
7616 if (obj->is_objArray()) {
7617 size_t sz = obj->size();
7618 HeapWord* end_card_addr =
7619 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
7620 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7621 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7622 _collector->_modUnionTable.mark_range(redirty_range);
7623 } else {
7624 _collector->_modUnionTable.mark(addr);
7625 }
7626 _collector->_ser_kac_preclean_ovflw++;
7627 } else {
7628 _collector->push_on_overflow_list(obj);
7629 _collector->_ser_kac_ovflw++;
7630 }
7631 }
7632 }
7633 }
7634
7635 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7636 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
7637
7638 // CMSParKeepAliveClosure: a parallel version of the above.
7639 // The work queues are private to each closure (thread),
7640 // but (may be) available for stealing by other threads.
7641 void CMSParKeepAliveClosure::do_oop(oop obj) {
7642 HeapWord* addr = (HeapWord*)obj;
7643 if (_span.contains(addr) &&
7644 !_bit_map->isMarked(addr)) {
7645 // In general, during recursive tracing, several threads
7646 // may be concurrently getting here; the first one to
7647 // "tag" it, claims it.
7648 if (_bit_map->par_mark(addr)) {
7649 bool res = _work_queue->push(obj);
7650 assert(res, "Low water mark should be much less than capacity");
7651 // Do a recursive trim in the hope that this will keep
7652 // stack usage lower, but leave some oops for potential stealers
7653 trim_queue(_low_water_mark);
7654 } // Else, another thread got there first
7655 }
7656 }
7657
7658 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7659 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
7660
7661 void CMSParKeepAliveClosure::trim_queue(uint max) {
7662 while (_work_queue->size() > max) {
7663 oop new_oop;
7664 if (_work_queue->pop_local(new_oop)) {
7665 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
7666 assert(_bit_map->isMarked((HeapWord*)new_oop),
7667 "no white objects on this stack!");
7668 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7669 // iterate over the oops in this oop, marking and pushing
7670 // the ones in CMS heap (i.e. in _span).
7671 new_oop->oop_iterate(&_mark_and_push);
7672 }
7673 }
7674 }
7675
7676 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
7677 CMSCollector* collector,
7678 MemRegion span, CMSBitMap* bit_map,
7679 OopTaskQueue* work_queue):
7680 _collector(collector),
7681 _span(span),
7682 _bit_map(bit_map),
7683 _work_queue(work_queue) { }
7684
7685 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
7686 HeapWord* addr = (HeapWord*)obj;
7687 if (_span.contains(addr) &&
7688 !_bit_map->isMarked(addr)) {
7689 if (_bit_map->par_mark(addr)) {
7690 bool simulate_overflow = false;
7691 NOT_PRODUCT(
7692 if (CMSMarkStackOverflowALot &&
7693 _collector->par_simulate_overflow()) {
7694 // simulate a stack overflow
7695 simulate_overflow = true;
7696 }
7697 )
7698 if (simulate_overflow || !_work_queue->push(obj)) {
7699 _collector->par_push_on_overflow_list(obj);
7700 _collector->_par_kac_ovflw++;
7701 }
7702 } // Else another thread got there already
7703 }
7704 }
7705
7706 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7707 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
7708
7709 //////////////////////////////////////////////////////////////////
7710 // CMSExpansionCause /////////////////////////////
7711 //////////////////////////////////////////////////////////////////
7712 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
7713 switch (cause) {
7714 case _no_expansion:
7715 return "No expansion";
7716 case _satisfy_free_ratio:
7717 return "Free ratio";
7718 case _satisfy_promotion:
7719 return "Satisfy promotion";
7720 case _satisfy_allocation:
7721 return "allocation";
7722 case _allocate_par_lab:
7723 return "Par LAB";
7724 case _allocate_par_spooling_space:
7725 return "Par Spooling Space";
7726 case _adaptive_size_policy:
7727 return "Ergonomics";
7728 default:
7729 return "unknown";
7730 }
7731 }
7732
7733 void CMSDrainMarkingStackClosure::do_void() {
7734 // the max number to take from overflow list at a time
7735 const size_t num = _mark_stack->capacity()/4;
7736 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
7737 "Overflow list should be NULL during concurrent phases");
7738 while (!_mark_stack->isEmpty() ||
7739 // if stack is empty, check the overflow list
7740 _collector->take_from_overflow_list(num, _mark_stack)) {
7741 oop obj = _mark_stack->pop();
7742 HeapWord* addr = (HeapWord*)obj;
7743 assert(_span.contains(addr), "Should be within span");
7744 assert(_bit_map->isMarked(addr), "Should be marked");
7745 assert(obj->is_oop(), "Should be an oop");
7746 obj->oop_iterate(_keep_alive);
7747 }
7748 }
7749
7750 void CMSParDrainMarkingStackClosure::do_void() {
7751 // drain queue
7752 trim_queue(0);
7753 }
7754
7755 // Trim our work_queue so its length is below max at return
7756 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
7757 while (_work_queue->size() > max) {
7758 oop new_oop;
7759 if (_work_queue->pop_local(new_oop)) {
7760 assert(new_oop->is_oop(), "Expected an oop");
7761 assert(_bit_map->isMarked((HeapWord*)new_oop),
7762 "no white objects on this stack!");
7763 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
7764 // iterate over the oops in this oop, marking and pushing
7765 // the ones in CMS heap (i.e. in _span).
7766 new_oop->oop_iterate(&_mark_and_push);
7767 }
7768 }
7769 }
7770
7771 ////////////////////////////////////////////////////////////////////
7772 // Support for Marking Stack Overflow list handling and related code
7773 ////////////////////////////////////////////////////////////////////
7774 // Much of the following code is similar in shape and spirit to the
7775 // code used in ParNewGC. We should try and share that code
7776 // as much as possible in the future.
7777
7778 #ifndef PRODUCT
7779 // Debugging support for CMSStackOverflowALot
7780
7781 // It's OK to call this multi-threaded; the worst thing
7782 // that can happen is that we'll get a bunch of closely
7783 // spaced simulated overflows, but that's OK, in fact
7784 // probably good as it would exercise the overflow code
7785 // under contention.
7786 bool CMSCollector::simulate_overflow() {
7787 if (_overflow_counter-- <= 0) { // just being defensive
7788 _overflow_counter = CMSMarkStackOverflowInterval;
7789 return true;
7790 } else {
7791 return false;
7792 }
7793 }
7794
7795 bool CMSCollector::par_simulate_overflow() {
7796 return simulate_overflow();
7797 }
7798 #endif
7799
7800 // Single-threaded
7801 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
7802 assert(stack->isEmpty(), "Expected precondition");
7803 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
7804 size_t i = num;
7805 oop cur = _overflow_list;
7806 const markOop proto = markOopDesc::prototype();
7807 NOT_PRODUCT(ssize_t n = 0;)
7808 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
7809 next = oop(cur->mark());
7810 cur->set_mark(proto); // until proven otherwise
7811 assert(cur->is_oop(), "Should be an oop");
7812 bool res = stack->push(cur);
7813 assert(res, "Bit off more than can chew?");
7814 NOT_PRODUCT(n++;)
7815 }
7816 _overflow_list = cur;
7817 #ifndef PRODUCT
7818 assert(_num_par_pushes >= n, "Too many pops?");
7819 _num_par_pushes -=n;
7820 #endif
7821 return !stack->isEmpty();
7822 }
7823
7824 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
7825 // (MT-safe) Get a prefix of at most "num" from the list.
7826 // The overflow list is chained through the mark word of
7827 // each object in the list. We fetch the entire list,
7828 // break off a prefix of the right size and return the
7829 // remainder. If other threads try to take objects from
7830 // the overflow list at that time, they will wait for
7831 // some time to see if data becomes available. If (and
7832 // only if) another thread places one or more object(s)
7833 // on the global list before we have returned the suffix
7834 // to the global list, we will walk down our local list
7835 // to find its end and append the global list to
7836 // our suffix before returning it. This suffix walk can
7837 // prove to be expensive (quadratic in the amount of traffic)
7838 // when there are many objects in the overflow list and
7839 // there is much producer-consumer contention on the list.
7840 // *NOTE*: The overflow list manipulation code here and
7841 // in ParNewGeneration:: are very similar in shape,
7842 // except that in the ParNew case we use the old (from/eden)
7843 // copy of the object to thread the list via its klass word.
7844 // Because of the common code, if you make any changes in
7845 // the code below, please check the ParNew version to see if
7846 // similar changes might be needed.
7847 // CR 6797058 has been filed to consolidate the common code.
7848 bool CMSCollector::par_take_from_overflow_list(size_t num,
7849 OopTaskQueue* work_q,
7850 int no_of_gc_threads) {
7851 assert(work_q->size() == 0, "First empty local work queue");
7852 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
7853 if (_overflow_list == NULL) {
7854 return false;
7855 }
7856 // Grab the entire list; we'll put back a suffix
7857 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
7858 Thread* tid = Thread::current();
7859 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
7860 // set to ParallelGCThreads.
7861 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
7862 size_t sleep_time_millis = MAX2((size_t)1, num/100);
7863 // If the list is busy, we spin for a short while,
7864 // sleeping between attempts to get the list.
7865 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
7866 os::sleep(tid, sleep_time_millis, false);
7867 if (_overflow_list == NULL) {
7868 // Nothing left to take
7869 return false;
7870 } else if (_overflow_list != BUSY) {
7871 // Try and grab the prefix
7872 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
7873 }
7874 }
7875 // If the list was found to be empty, or we spun long
7876 // enough, we give up and return empty-handed. If we leave
7877 // the list in the BUSY state below, it must be the case that
7878 // some other thread holds the overflow list and will set it
7879 // to a non-BUSY state in the future.
7880 if (prefix == NULL || prefix == BUSY) {
7881 // Nothing to take or waited long enough
7882 if (prefix == NULL) {
7883 // Write back the NULL in case we overwrote it with BUSY above
7884 // and it is still the same value.
7885 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
7886 }
7887 return false;
7888 }
7889 assert(prefix != NULL && prefix != BUSY, "Error");
7890 size_t i = num;
7891 oop cur = prefix;
7892 // Walk down the first "num" objects, unless we reach the end.
7893 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
7894 if (cur->mark() == NULL) {
7895 // We have "num" or fewer elements in the list, so there
7896 // is nothing to return to the global list.
7897 // Write back the NULL in lieu of the BUSY we wrote
7898 // above, if it is still the same value.
7899 if (_overflow_list == BUSY) {
7900 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
7901 }
7902 } else {
7903 // Chop off the suffix and return it to the global list.
7904 assert(cur->mark() != BUSY, "Error");
7905 oop suffix_head = cur->mark(); // suffix will be put back on global list
7906 cur->set_mark(NULL); // break off suffix
7907 // It's possible that the list is still in the empty(busy) state
7908 // we left it in a short while ago; in that case we may be
7909 // able to place back the suffix without incurring the cost
7910 // of a walk down the list.
7911 oop observed_overflow_list = _overflow_list;
7912 oop cur_overflow_list = observed_overflow_list;
7913 bool attached = false;
7914 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
7915 observed_overflow_list =
7916 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7917 if (cur_overflow_list == observed_overflow_list) {
7918 attached = true;
7919 break;
7920 } else cur_overflow_list = observed_overflow_list;
7921 }
7922 if (!attached) {
7923 // Too bad, someone else sneaked in (at least) an element; we'll need
7924 // to do a splice. Find tail of suffix so we can prepend suffix to global
7925 // list.
7926 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
7927 oop suffix_tail = cur;
7928 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
7929 "Tautology");
7930 observed_overflow_list = _overflow_list;
7931 do {
7932 cur_overflow_list = observed_overflow_list;
7933 if (cur_overflow_list != BUSY) {
7934 // Do the splice ...
7935 suffix_tail->set_mark(markOop(cur_overflow_list));
7936 } else { // cur_overflow_list == BUSY
7937 suffix_tail->set_mark(NULL);
7938 }
7939 // ... and try to place spliced list back on overflow_list ...
7940 observed_overflow_list =
7941 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
7942 } while (cur_overflow_list != observed_overflow_list);
7943 // ... until we have succeeded in doing so.
7944 }
7945 }
7946
7947 // Push the prefix elements on work_q
7948 assert(prefix != NULL, "control point invariant");
7949 const markOop proto = markOopDesc::prototype();
7950 oop next;
7951 NOT_PRODUCT(ssize_t n = 0;)
7952 for (cur = prefix; cur != NULL; cur = next) {
7953 next = oop(cur->mark());
7954 cur->set_mark(proto); // until proven otherwise
7955 assert(cur->is_oop(), "Should be an oop");
7956 bool res = work_q->push(cur);
7957 assert(res, "Bit off more than we can chew?");
7958 NOT_PRODUCT(n++;)
7959 }
7960 #ifndef PRODUCT
7961 assert(_num_par_pushes >= n, "Too many pops?");
7962 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
7963 #endif
7964 return true;
7965 }
7966
7967 // Single-threaded
7968 void CMSCollector::push_on_overflow_list(oop p) {
7969 NOT_PRODUCT(_num_par_pushes++;)
7970 assert(p->is_oop(), "Not an oop");
7971 preserve_mark_if_necessary(p);
7972 p->set_mark((markOop)_overflow_list);
7973 _overflow_list = p;
7974 }
7975
7976 // Multi-threaded; use CAS to prepend to overflow list
7977 void CMSCollector::par_push_on_overflow_list(oop p) {
7978 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
7979 assert(p->is_oop(), "Not an oop");
7980 par_preserve_mark_if_necessary(p);
7981 oop observed_overflow_list = _overflow_list;
7982 oop cur_overflow_list;
7983 do {
7984 cur_overflow_list = observed_overflow_list;
7985 if (cur_overflow_list != BUSY) {
7986 p->set_mark(markOop(cur_overflow_list));
7987 } else {
7988 p->set_mark(NULL);
7989 }
7990 observed_overflow_list =
7991 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
7992 } while (cur_overflow_list != observed_overflow_list);
7993 }
7994 #undef BUSY
7995
7996 // Single threaded
7997 // General Note on GrowableArray: pushes may silently fail
7998 // because we are (temporarily) out of C-heap for expanding
7999 // the stack. The problem is quite ubiquitous and affects
8000 // a lot of code in the JVM. The prudent thing for GrowableArray
8001 // to do (for now) is to exit with an error. However, that may
8002 // be too draconian in some cases because the caller may be
8003 // able to recover without much harm. For such cases, we
8004 // should probably introduce a "soft_push" method which returns
8005 // an indication of success or failure with the assumption that
8006 // the caller may be able to recover from a failure; code in
8007 // the VM can then be changed, incrementally, to deal with such
8008 // failures where possible, thus, incrementally hardening the VM
8009 // in such low resource situations.
8010 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8011 _preserved_oop_stack.push(p);
8012 _preserved_mark_stack.push(m);
8013 assert(m == p->mark(), "Mark word changed");
8014 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8015 "bijection");
8016 }
8017
8018 // Single threaded
8019 void CMSCollector::preserve_mark_if_necessary(oop p) {
8020 markOop m = p->mark();
8021 if (m->must_be_preserved(p)) {
8022 preserve_mark_work(p, m);
8023 }
8024 }
8025
8026 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8027 markOop m = p->mark();
8028 if (m->must_be_preserved(p)) {
8029 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8030 // Even though we read the mark word without holding
8031 // the lock, we are assured that it will not change
8032 // because we "own" this oop, so no other thread can
8033 // be trying to push it on the overflow list; see
8034 // the assertion in preserve_mark_work() that checks
8035 // that m == p->mark().
8036 preserve_mark_work(p, m);
8037 }
8038 }
8039
8040 // We should be able to do this multi-threaded,
8041 // a chunk of stack being a task (this is
8042 // correct because each oop only ever appears
8043 // once in the overflow list. However, it's
8044 // not very easy to completely overlap this with
8045 // other operations, so will generally not be done
8046 // until all work's been completed. Because we
8047 // expect the preserved oop stack (set) to be small,
8048 // it's probably fine to do this single-threaded.
8049 // We can explore cleverer concurrent/overlapped/parallel
8050 // processing of preserved marks if we feel the
8051 // need for this in the future. Stack overflow should
8052 // be so rare in practice and, when it happens, its
8053 // effect on performance so great that this will
8054 // likely just be in the noise anyway.
8055 void CMSCollector::restore_preserved_marks_if_any() {
8056 assert(SafepointSynchronize::is_at_safepoint(),
8057 "world should be stopped");
8058 assert(Thread::current()->is_ConcurrentGC_thread() ||
8059 Thread::current()->is_VM_thread(),
8060 "should be single-threaded");
8061 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8062 "bijection");
8063
8064 while (!_preserved_oop_stack.is_empty()) {
8065 oop p = _preserved_oop_stack.pop();
8066 assert(p->is_oop(), "Should be an oop");
8067 assert(_span.contains(p), "oop should be in _span");
8068 assert(p->mark() == markOopDesc::prototype(),
8069 "Set when taken from overflow list");
8070 markOop m = _preserved_mark_stack.pop();
8071 p->set_mark(m);
8072 }
8073 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
8074 "stacks were cleared above");
8075 }
8076
8077 #ifndef PRODUCT
8078 bool CMSCollector::no_preserved_marks() const {
8079 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
8080 }
8081 #endif
8082
8083 // Transfer some number of overflown objects to usual marking
8084 // stack. Return true if some objects were transferred.
8085 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
8086 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
8087 (size_t)ParGCDesiredObjsFromOverflowList);
8088
8089 bool res = _collector->take_from_overflow_list(num, _mark_stack);
8090 assert(_collector->overflow_list_is_empty() || res,
8091 "If list is not empty, we should have taken something");
8092 assert(!res || !_mark_stack->isEmpty(),
8093 "If we took something, it should now be on our stack");
8094 return res;
8095 }
8096
8097 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
8098 size_t res = _sp->block_size_no_stall(addr, _collector);
8099 if (_sp->block_is_obj(addr)) {
8100 if (_live_bit_map->isMarked(addr)) {
8101 // It can't have been dead in a previous cycle
8102 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
8103 } else {
8104 _dead_bit_map->mark(addr); // mark the dead object
8105 }
8106 }
8107 // Could be 0, if the block size could not be computed without stalling.
8108 return res;
8109 }
8110
8111 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
8112
8113 switch (phase) {
8114 case CMSCollector::InitialMarking:
8115 initialize(true /* fullGC */ ,
8116 cause /* cause of the GC */,
8117 true /* recordGCBeginTime */,
8118 true /* recordPreGCUsage */,
8119 false /* recordPeakUsage */,
8120 false /* recordPostGCusage */,
8121 true /* recordAccumulatedGCTime */,
8122 false /* recordGCEndTime */,
8123 false /* countCollection */ );
8124 break;
8125
8126 case CMSCollector::FinalMarking:
8127 initialize(true /* fullGC */ ,
8128 cause /* cause of the GC */,
8129 false /* recordGCBeginTime */,
8130 false /* recordPreGCUsage */,
8131 false /* recordPeakUsage */,
8132 false /* recordPostGCusage */,
8133 true /* recordAccumulatedGCTime */,
8134 false /* recordGCEndTime */,
8135 false /* countCollection */ );
8136 break;
8137
8138 case CMSCollector::Sweeping:
8139 initialize(true /* fullGC */ ,
8140 cause /* cause of the GC */,
8141 false /* recordGCBeginTime */,
8142 false /* recordPreGCUsage */,
8143 true /* recordPeakUsage */,
8144 true /* recordPostGCusage */,
8145 false /* recordAccumulatedGCTime */,
8146 true /* recordGCEndTime */,
8147 true /* countCollection */ );
8148 break;
8149
8150 default:
8151 ShouldNotReachHere();
8152 }
8153 }